GeoMan's Southern California Weekend Storm Forecast

[Geomagnetic Man]

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org For Official Information please refer to the NHC and NWS products.

WINTER STORM ANDREW
AREA FORECAST DISCUSSION
ONTARIO CA
Wednesday, October 12, 2005 2:34 PM

DISCUSSION ... FOR ALL OF SOUTHWESTERN CALIFORNIA INCLUDING ALL OF
ORANGE COUNTY ... SOUTHERN LOS ANGELES COUNTY ... WESTERN RIVERSIDE
COUNTY ... AND SOUTHWESTERN SAN BERNARDINO COUNTY ...

SYNOPSIS....Winter Storm Andrew has showed up in the analysis. It should
form off our coast, and slam us during the latter part of the weekend,
into early next week. Stay tuned!

...SHORT RANGE DISCUSSION...

THE RAIN CHANCES...Winter Storm Andrew will be developing off the
Central-Southern California coastline later this week. It will be an
impressive storm system. Rain chances look good for now out of Andrew.
Usually we see a cold front come in first, giving us a massive downpour
of all the rain, but that will not be the case. The cold front will form
to the east of here, and move away quickly. What we are very interested
in is the moisture content, with the cold air aloft. that could set a
stage for lots of rain. Based on current analysis rain could start as
early as Saturday night, but get more numerous throughout the night
into Sunday morning. The rain could last all the way until Monday
evening, but we will keep you posted on this. A flood watch will
probably be needed with Andrew.

THE THUNDERSTORM CHANCES... Andrew's chances for thunderstorms will be
quite interesting. The thunderstorms chances will start on Saturday
night when the moisture arrives. The dynamics for that period will not
be all that strong. We have a -18 degrees Celsius temperature at 500MB
or 17,000 feet. This coMBined with a 4 degree C temp at 850 MB or 3,000
feet will give a total of 22 degrees. This doesn't really fit the charts
we have for any dangerous thunderstorms. Keep in mind, all thunderstorms
are dangerous, but the really severe ones we rarely see in Southern
California is what I'm talking about. I will introduce a Slight Chance
of Thunderstorms on Saturday Night. Now on Sunday Morning at sunrise
the nuMBers change. We have a -22 degrees Celsius temperature at 500MB.
That combined with a 6 degree C temp at 850 MB will give a total of 28
degrees. That gives you a higher number of thunderstorm probabilities.
By looking at our charts, combined with the moisture we will have
around, it looks like it lands in the Strong Thunderstorm Category,
40-50% chance, and a Low risk at being severe. So from that, you can
really tell that the chance on Sunday morning are pretty flat out
there. Now lets look at 11am Sunday morning. The sun will be up high,
so the ground will start to heat. That will warm the lower levels, and
give us a gradient change. This change warrants thunderstorms. Let's
look at the numbers shall we? A temp of -24 degrees Celsius at 500mb,
with a temp of 6 degree C temp at 850mb, gives an impressive 30 degree
temp difference. That's higher than sunrise Sunday morning as you can
see. This combined with 80% gives a great chance of thunderstorm
development. Also out of this development will be the chance of Severe
Thunderstorms, with a 65% chance at that, and also a slight risk
category severe thunderstorms. A slight risk has been seen, so the next
forecast will determine the chances of Tornadoes from this as it could
very well be possible. These dynamics go into Sunday afternoon, and
evening, into the night! Next forecast will determine what could happen
on Monday of Next week, but for now, we will leave it at that. Monday
could be a repeat of Sunday.

WIND CHANCES... Winter Storm Andrew will not be a hurricane like
Hurricane Andrew, not even winds that close will be recorded from this.
The dynamics needed for the bow echo type systems, the frontal winds
will not hit the forecast area this time as far as current trends look.
So winds do not look like a problem, and no wind watch will be needed at
this time.


MEDIUM RANGE DISCUSSION...After Andrew, all looks calm again.


GeoMan

[wxmann_91]

WOW, our first winter storm. Should be interesting.

Saw it on TWC for the first time this morning, totally forgot about it, thanks for the forecast.

From the NWS San Diego AFD:

EXPECT WIDESPREAD COOLING WITH TEMPERATURES BELOW SEASONAL NORMALS AND...DEPENDING ON WHERE THE UPPER LOW EVENTUALLY ENDS UP...COULD BE SHOWERS OVER THE AREA SUNDAY AND MONDAY.

[WindRunner]

Do they actually name the storms, or is that something you do, Geoman?

[weatherlover427]

I think it's something that he or someone else does because AFAIK only hurricanes and tropical storms get names. I could be wrong though, it might be a new idea the NWS out here is trying that I haven't heard of yet...

[Geomagnetic Man]

I name them yes. I had this idea of doing so. Andrew is first, then its Bart, then Carolyn. I have a whole list ready to go! The storms that effect the Southern California area with any type of cold front, or cold core will be named. Andrew is the first, and it looks like it will pack a powerful punch in some places.

GeoMan James

[wxmann_91]

The latest AFD from NWS Los Angeles is interesting:

CONSIDERABLE UNCERTAINTY ENTERS THE FORECAST BEGINNING SATURDAY
NIGHT...AND THEY ALL HAVE TO DO WITH THE EXACT PATH THIS STRONG
CUTTING OFF UPPER LEVEL LOW TAKES. MODELS VARY FROM THE GFS AND
UKMET PLACING IT OVER THE SOUTHEASTERN DESERTS BY SUNDAY
MORNING...TO THE NAM WHICH PLACES IT OVER LA COUNTY...TO THE ECMWF
WHICH PLACES IT OFF OF POINT CONCEPTION. SO THE RANGE OF SOLUTIONS
VARIES FROM A HIGH WIND/SANTA ANA EVENT AND WARMER TEMPERATURES
(GFS/UKMET)...TO NOT AS MUCH WIND...POSSIBLY SOUTHERLY FLOW...A MUCH
GREATER CHANCE OF PRECIPITATION...AND COLDER TEMPERATURES
(NAM/ECMWF). AT THIS POINT AND AFTER COORDINATION WITH SURROUNDING
OFFICES...WILL GO WITH A SLIGHT CHC OF SHOWERS MOST EVERYWHERE BY
SUNDAY MORNING...WITH A LITTLE HIGHER CHANCES IN THE MOUNTAINS. BOTH
THE GFS AND NAM DO INDICATE SNOW LEVELS DOWN TO AROUND 6500 FT. I
WON'T GO THAT LOW AND INSTEAD KEEP THEM 7000 FT OR ABOVE FOR NOW.
THERE COULD EVEN BE SOME THUNDERSTORMS AROUND IF THE PATH OF THE LOW
IS CLOSER TO THE NAM...HOWEVER I WON'T MENTION THOSE YET IN THE
FORECAST.

Unfortunately, it means that there is a chance that this could be yet another bust.

[Geomagnetic Man]

Here's today's I wrote up.
------------------------------------
WINTER STORM ANDREW

AREA FORECAST DISCUSSION
ONTARIO CA
Thursday, October 13, 2005 5:33 PM

DISCUSSION ... FOR ALL OF SOUTHWESTERN CALIFORNIA INCLUDING ALL OF ORANGE COUNTY ... SOUTHERN LOS ANGELES COUNTY ... WESTERN RIVERSIDE COUNTY ... AND SOUTHWESTERN SAN BERNARDINO COUNTY ...

...SHORT RANGE DISCUSSION...

MODEL ANALYSIS...Winter Storm Andrew will be developing over Northern California tomorrow, and sliding southward toward us. The models really differ on the track of Andrew right now. The ETA shows it over the forecast area, and the GFS shows it over the Eastern sections, mostly out of the forecast area. This forecast today will be very hard, as it always is with these cutoff systems. It could go from Santa Ana Winds to Thunderstorms, which ever model is correct. Decided to compare the 500MB RH and the 250MB RH to current satellite images. GFS and ETA were very similar, but the locations, and shapes in the ETA were actually alot better than the GFS so now we will go with the ETA.

THE RAIN CHANCES...Winter Storm Andrew could give moderate amounts of rain to us. The rain looks to start from the northern forecast area during the 11pm hr on Saturday, and spread south there after, covering the rest of the forecast area after midnight. Let's break down the atmosphere for you. Saturday Night at 11pm, we will have 70%-80% RH, or Relative Humidity at 850MB or 5,000 feet across the entire forecast area, and a sharp gradient from dry air, to moist air at 700MB across the San Gabriel Mountains. This will mark the start of the rain chances. In fact, by looking at the 500 MB vort, which means the higher value the faster the air is being force upwards. The faster the air being forced upwards, the stronger the rain, and storm event. The leading edge of this vort comes in like a front after midnight, and quickly moves south. We could see a blast of heavy rain from this leading edge around 1 or 2am early Sunday Morning. After that leading edge we will now talk about the 5am hour. Sunday Morning at 5am dynamics look like this. 850MB RH will be at an impressive 90%. This combined with a 700MB RH of 80% will give way to rain. We could get good measure-able rain at this hour. By 11am Sunday Morning 850MB RH goes down to 80%, with an 80% RH at 700MB, giving that the best chance of rain so far in this forecast. maybe over 1/4 inch of rain in places possible. On Sunday Evening at 5pm, the moisture at 850MB RH goes to 70%, and the 700MB stays at 80%, with still a good chance of rain, however better than Sunday at sunrise, but not better than noon Sunday Afternoon. Tomorrow's forecast will have Monday included as well.

THE THUNDERSTORM CHANCES... Andrew's chances for thunderstorms will begin Saturday Night after midnight. The 500MB vort shows a solid line of upper 30's moving across the forecast area by then. a weak-strong line of thunderstorms could form then, and press southward throughout the night. by 5am, this line of action should be well south, in the San Diego area. Otherwise the dynamics at 5am over our forecast area look good for thunderstorms. We will have a -21 degree Celsius temperature at 17,000 feet, combined with a 6 degree Celsius temperature at 5,000 feet. This with an 80% RH at 850MB and a CAPE of 250-300 across the forecast area gives way to a value in the charts high enough to warrant the slight risk severe thunderstorm category, severe thunderstorms possible, and a 60% chance of thunderstorms in this time slot. A Severe Thunderstorm Watch might be needed if analysis continues on this run. At 11am Sunday Morning the dynamics show values stronger than the 5am hour. This might yelled the moderate severe category, and last throughout the day on Sunday. Thunderstorms may produce hail, with a possible chance of a funnel cloud, or brief weak tornado as the cold air moves directly overhead.

WIND CHANCES... Winter Storm Andrew will not be a hurricane like Hurricane Andrew, not even winds that close will be recorded from this. The dynamics needed for the bow echo type systems, the frontal winds will not hit the forecast area this time as far as current trends look. So winds do not look like a problem, and no wind watch will be needed at this time.


MEDIUM RANGE DISCUSSION...After Andrew, all looks calm again.

GeoMan James

[Geomagnetic Man]

Excellent! LATEST model runs have confirmed my forecast. Yesterday's model runs showed the storm center east of here, however I decided to try something. Matching the models with current satellite data, It showed me that the GFS was the right model,, but the location of the center should have been more west over Los Angeles, and surrounding eastern cities. Today's model run shows just that. The GFS now has it over where I knew it should have been in th first place. Another forecast will come out later today on this. This looks like a really nice storm system, especially for this time of year!

GeoMan James

[Geomagnetic Man]

WINTER STORM ANDREW

CATEGORY 3 ISSUED TO WINTER STORM ANDREW

AREA FORECAST DISCUSSION
ONTARIO CA
Friday, October 14, 2005 1:51 PM

DISCUSSION ... FOR ALL OF SOUTHWESTERN CALIFORNIA INCLUDING ALL OF ORANGE COUNTY ... SOUTHERN LOS ANGELES COUNTY ... WESTERN RIVERSIDE COUNTY ... AND SOUTHWESTERN SAN BERNARDINO COUNTY ...

SYNOPSIS....Winter Storm Andrew showed up in Analysis during the early part of the week, and finally showed up on time on satellite images. Winter Storm Andrew has officially developed, and is on track.

PRE-STORM FACTS: We use this section to tell you the conditions before the storm. If we tell you a condition and it comes true when we say it, expect the storm to be on track! The condition will not be set yet.

...SHORT RANGE DISCUSSION...

MODEL ANALYSIS...Winter Storm Andrew has followed the GFS analysis better than the ETA thus far, so decided to go with that as the forecasting model of choice. Dynamics in this look okay for rain, but much better chances of Thunderstorms than rain event with Andrew.

THE RAIN CHANCES...Winter Storm Andrew will be sliding right across the eastern forecast areas. Though the models have been playing with the location a bit, only error is 50 miles, nd that is crucial to what will actually happen. If Andrew slides more west, we will get a better chance of rain being the flow will be coming from southerly direction, where alot of moisture looms. Currently the track of Andrew does not put us in a favorable position for huge downpours like some of the major winter storms we've seen, but remember, it's only Mid-October! We can take this for what it's got. The rain should start scattered, and stay scattered from 11pm Saturday Night, to Tuesday sometime. This is a large system, and it will cover a lot of ground, and air. A flood watch may, or may not be needed, that will be determined tomorrow.

THE THUNDERSTORM CHANCES... Andrew's chances for thunderstorms will begin Saturday Night after midnight. 500MB vort still is on track, showing a solid line of mid 30 values pouring into the area then. It's on the leading edge of the low level moisture, so this looks like a mini dry line front of some kind. Let's again, break down for you what will happen throughout the forecasting period like we have been doing. Let's not get all out of hand, so we will make this nice and short. Sunday Morning there is a chance of Thunderstorms as the Cold Air Aloft moves direct overhead. During that time, you can expect numerous thunderstorms across the forecast area. By Sunday Afternoon the heating of the day, if it can happen will allow the low levels to heat up, and this combined with very cold air aloft, and steep lapse rates will generate the powerhouse needed for big time thunderstorms. Out of these Thunderstorms a cold core funnel cloud, or brief weak tornado may be possible. This thunderstorms should move slowly to the West and Northwest throughout the day. Monday looks like a repeat of Sunday with cold air still aloft, and enough moisture, and lapse rates steepening to allow the same breeding ground for thunderstorms to form. Tuesday could be the same, but we will talk about this tomorrow.

WIND CHANCES... Winter Storm Andrew will not be a hurricane like Hurricane Andrew, not even winds that close will be recorded from this. The dynamics needed for the bow echo type systems, the frontal winds will not hit the forecast area this time as far as current trends look. So winds do not look like a problem, and no wind watch will be needed at this time.


MEDIUM RANGE DISCUSSION...After Andrew, all looks calm again.

ACTIVATED ALERTS...ACTIVATED!

Winter Storm Andrew is a category 3 type storm. A category 3 in my charts means Rain, and Thunderstorms, with minor flooding expected.

GeoMan James

[TT-SEA]

Your "Category 3" is looking pretty much like a weak trough.

Pretty generous with your rankings there!!

Whats a Category 1?? This may not even qualify for that description.

[Geomagnetic Man]

Category 1 is weak showery scattered type event. A no, the storm is not starting to look like a weak trough. Read the models if you know how to please. Right now, yes it looks like a trough, but it really looks like a low pressure will form on the extreme southern end of it as it dips down into Southern California. Watch what the next 24 hrs will do to it!

GeoMan James

P.S. , actually the category system is NOT CURRENT location and strength, it's a forecast of what it will be when it hits Southern California, where I forecast

[TT-SEA]

I am in Seattle and I am experiencing your storm now with real wind and rain.

I would not call this a "Category 3" even up here. And we are getting much more than you will.

The latest NAM shows absolutely no precipitation for the L.A. or San Diego areas.

This will likely produce Santa Ana winds but not much actual rain.

[TT-SEA]

Total precipitation through Monday morning:

[weatherlover427]

Tim, enough is enough. You have to realize that there are things called "model differences". I have read many of your posts over my time here at this board and to me, you come across as quite harsh in some of them. Types of posts like these are why I rarely post on S2K now a days. It was better back in 2003 before all the constant bickering and flaming started, such as this.

But you have to realize that there are other models out there - the UKMet, the GFS, the ECMWF, etc. You can't just run by the ETA (NAM) and expect your forecasts to be right 100% of the time with no exceptions.

I think that you should respect GeoMan James's opinions and thoughts, as we are all entitled to our own. I respect you for yours, but I may not always agree with them, which is the point that I am trying to convey here. Maybe thinking some more about where the original poster might be coming from before putting finger to keyboard would help.

[Geomagnetic Man]

Tim, yes the storm doesn't seem like a Category 3 type I call it because I don't forecast for the seattle area. I forecast for when the storm is down here. Look on the models, and get back to me. The storm is a trough right now, but as you see it turns into a closed low right over Southern California. Indicates strengthening in the dynamics, and gives the cold pool aloft. I saw something like this back on November 23rd I believe 2004. Came from the north, and produced numerous Thunderstorms at night, followed by heavy rain, and santa ana conditions with the rain. It was a true hurricane force wind with rain. Just simply amazing! Depending on the track the model shows in the next 2 hrs will determine if it will be a soaker with barely any wind, or a fierce Wet Santa Ana condition like last year.

FYI Heres my Category Tables.

Category 1- Weak Showers harmless wind

Category 2- Rain with harmless wind

Category 3- Rain and Thunderstorms with MINOR flooding, and MINOR Wind Concerns

Category 4- Rain and Thunderstorms with Major Flooding, and Major Wind Concerns

Category 5- Intense Thunderstorms with Bow Echo type structures, and Severe Winds, and Severe Flooding.

So this storm when it hits California can either be a Category 3 or 4 storm. This does not have the power for a Category 5 because of the non-existance of a major frontal boundary. Next model runs will determine the Category. For now, it remains a Category 3

GeoMan James

[wxmann_91]

Tim, enough is enough. You have to realize that there are things called "model differences". I have read many of your posts over my time here at this board and to me, you come across as quite harsh in some of them. Types of posts like these are why I rarely post on S2K now a days. It was better back in 2003 before all the constant bickering and flaming started, such as this.

But you have to realize that there are other models out there - the UKMet, the GFS, the ECMWF, etc. You can't just run by the ETA (NAM) and expect your forecasts to be right 100% of the time with no exceptions.

I think that you should respect GeoMan James's opinions and thoughts, as we are all entitled to our own. I respect you for yours, but I may not always agree with them, which is the point that I am trying to convey here. Maybe thinking some more about where the original poster might be coming from before putting finger to keyboard would help.

Great post weatherlover427.

Last night the AFD from NWS San Diego (man I should've saved that one) mentioned the possibility that as the system exits on Tuesday, there is the possibility that it could draw up some deep subtropical moisture. They wrote that "there is the possibility of .75-1.5 inches of rain on Tuesday", but that "it is too early to raise the QPF". Another thing they mentioned this morning was that the GFS could be too quick in lifting this out.

A hundred miles west of where it is progged to go, and we could be dealing with 2 inches of rain along the coast easily from the period Saturday night - Tuesday. It definately bears watching.

[weatherlover427]

Here is that AFD that you mentioned:

AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN DIEGO CA 920 PM PDT THU OCT 13 2005

.SYNOPSIS...HIGH PRESSURE ALOFT AND WEAK OFFSHORE FLOW WILL BRING ANOTHER SUNNY AND WARM DAY FRIDAY. UPPER LEVEL LOW PRESSURE APPROACHING FROM THE NORTHWEST WILL CAUSE A DEEPENING MARINE LAYER AND COOLING SATURDAY. THE LOW WILL BRING MUCH COOLER WEATHER...LOCAL GUSTY WINDS AND A CHANCE OF SHOWERS AND THUNDERSTORMS SUNDAY INTO TUESDAY. FAIR AND WARMER DURING THE SECOND HALF OF NEXT WEEK.

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

NO MARINE LAYER LOW CLOUDS THIS EVENING AS WEAK OFFSHORE FLOW CONTINUES. STILL EXPECTING AN AREA OF STRATUS TO FORM OVER THE SOUTHERN SAN DIEGO COUNTY COAST LATE TONIGHT DUE TO SAN CLEMENTE ISLAND WAKE TURBULENCE. THAT WILL LIKELY CAUSE PATCHY DENSE FOG IN THAT AREA AS WELL. INVERSION IN THE PM SOUNDING WAS AT 1500 FEET...BUT EXPECT THAT TO LOWER TO 800 FEET OVERNIGHT AS WINDS RELAX AND AIR COOLS.

HIGH PRESSURE ALOFT WILL CONTINUE THROUGH FRI. THERE WILL BE LOCAL GUSTY WINDS THROUGH AND BELOW MOUNTAIN CANYONS AND PASSES...MAINLY IN SAN COUNTY FRI MORNING. SUNNY AND WARM FRIDAY.

THE TROUGH IS STILL FORECAST TO CLOSE OFF NEAR SRN CA SUN. EXPECT DEEPENING MOISTURE SUN WITH MUCH STRONGER WINDS ALOFT AND ONSHORE FLOW AND COOLING ALOFT. EARLIEST START OF LIGHT SHOWERS SHOULD BE EARLY SUNDAY MORNING AS THE 554 LOW SETTLES OVER SCALIF. THE COLDER AIR ALOFT COULD PRODUCE THUNDERSTORMS SUN AFTERNOON. COOLER SAT AND MUCH COOLER SUN. THE SNOW LEVEL SHOULD BE ABOUT 6500-7000 SUN. THE 2 DAY SUN/MON RAINFALL TOTALS SHOULD REMAIN UNDER ONE HALF INCH MOST AREAS.

THE LOW WILL SLOWLY DRIFT SW...THEN MOVE BACK OVER THE AREA ON TUE. AS IT COMES WEST AGAIN...IT COULD TAP SUBTROPICAL MOISTURE AND BRING .75 TO 1.5 INCH RAINS ON TUE DUE TO THE INITIAL PLUME AND THE WRAP AROUND MOISTURE. TOO EARLY TO UP QPF...BUT THIS PATTERN BEARS WATCHING.

It can be found at this link. (time sensitive)

If the NWS says it; it's possible (they are right most of the time "note the word MOST").

[TT-SEA]

No offense was meant by my post. None at all. Sorry for my unintended tone.

This storm was originally supposed to turn south before reaching Western Washington. It looked very impressive earlier for SoCal. Now it is moving through Washington. It is dumping most of its moisture out here and in Oregon.

This makes it more of an "insider slider" now.

I lived in San Diego for 12 years until last spring. I have watched MANY of these storms as well. Part of the reason that we moved to Seattle was to be more in the "line of fire". Actually that was MY reason. My wife does not really care about weather. She just loves all the trees and the lush green landscape.

I see the latest GFS does show a little rain down there over the weekend. Still could happen.

[TT-SEA]

I see that AFD was written by Ted Mackechnie.

Take what that guy says with a grain of salt. He likes to be over-dramatic. He drove me nuts somtimes when I lived down there.

[Geomagnetic Man]

Tim, none taken, Seattle I would think was in the line of fire as well. You have a number of things like Southern California. You have that Major Fault Slip that is happening as I write this to you. The fault is slowly bending off the coast, started a few months ago, and it could snap. Same here, southern california's San Andreas Fault could go. Line of fire for many things, however, I would want to move somewhere between San Francisco, and the Oregon Border, along the coast. I see that area get slammed alot, lol.