SE TX / SW LA - Heavy rains this week-Tues. and Fri???

[vbhoutex]

There have been some reports of pea to dime sized hail in the Houston vicinity from the cell currently moving through down there. However, there is no warning for it at the moment (which is strange since it is obviously right on the "edge" of being severe). Besides that storm, it now looks like another strong cell will be moving in from the NW. This one may also produce some hail..possibly closer to my area and in the northern part of the county. It will be interesting to see if this one gets a warning.

Just what are the severe limits you think are used to decide when a storm is severe and should be warned?

[Extremeweatherguy]

There have been some reports of pea to dime sized hail in the Houston vicinity from the cell currently moving through down there. However, there is no warning for it at the moment (which is strange since it is obviously right on the "edge" of being severe). Besides that storm, it now looks like another strong cell will be moving in from the NW. This one may also produce some hail..possibly closer to my area and in the northern part of the county. It will be interesting to see if this one gets a warning.

Just what are the severe limits you think are used to decide when a storm is severe and should be warned?

0.75" diameter hail, and/or 58mph+ wind gusts and/or a tornado. Those are the official severe limits.

At the time of this post, the radar estimates were showing possible hail up to penny to quarter size in that area (which is within the severe limit) and hail up to dime sized was already being reported on the ground. I have seen plenty of weaker storms than that one get warnings. The storm must have finally broken that "edge" of severe though, because minutes later a warning was finally issued on it in SE Harris county (which was just as that second line began to move into NW sections of the county).

[KatDaddy]

Thats per hour which means the bucket would need to dump 64 times in one hour. I would have picked up .60 per minute. With the instaneous flooding of roads and fields its possible. However I will continue to investigate this reading. I had another discussion on the channel 11 board.

Did anyone else recieve extremely high rainfall rates during the severe storm?

[jeff]

Highest rainfall rate I saw was .98 in 15 minutes on the upper end of Brays Bayou (Hwy 6 gage). A .6 per minute rainfall rate is very extreme...and given the moisture profiles I would question such a value (PWS were in the 1.3 to 1.5 in range). If it did rain .6 per minute it must of only lasted a minute or less as the overall total would be very high even for 5 minutes.

A recording of the HCOEM gage netwrok can be found at http://www.hcoem.org along with channel stream stages.

[KatDaddy]

Thanks for the input Jeff. I totally agree. I have a tech support question into Davis to verify how the rainfall rate is calculated. From what I have read its based on the tipping of the bucket Perhaps .60" a minute lasted 30 seconds. Its quite questionable and I hope to get some feedback from Davis. I picked up 2.65" for the entire day.
I will let you know what I hear from Davis. When I got yesterday and saw the max rainfall rate I had to look three times to make sure the graph was set to rainfall rate and make sure the console also displayed 38.40".

[PTrackerLA]

That seems like a very high rainfall rate but who knows? About 5 years ago we had a summer thunderstorm that was produced over 5-6" of rain in less than an hour at my house. My street had 3' of water in it and I had never seen it flood before or haven't seen it flood since. I couldn't believe how hard it rained and how much we received in such a short time but I guess conditions were just right for an excessive rainfall.

Anyways, we didn't have the flooding rains with this system as the heaviest storms stayed offshore but it was definately a good soaking of 1"-1.5" that was much needed. Rainfall is just about normal now for the year area-wide so hopefully we won't have a dry spring that seems to be common in recent years. Now it's time for a great weekend weather-wise with more showers next week!

[Extremeweatherguy]

12z GFS indicates another possible severe threat next Thursday or Friday...

http://www.nco.ncep.noaa.gov/pmb/nwprod ... _180.shtml

We will have to watch this one closely.

[KatDaddy]

Mystery resolved by another poster over at the Channel 11 board:

Hey KayDaddy,

Tuesday at 10:04pm, my VP2 recorded a high rain rate of 16.94 inches per hour in one 5 minute sampling period and 15.40 inches per hour in the next. I was home and from what I saw, it was quite accurate. I had 0.56 inches total fall in that 5 minute period

It only takes 2 bucket tips to create any one rain rate reading. It's the time in between that makes the difference.

If you get a direct downdraft in the rain funnel, you can get in a situation where the rain tips the bucket over and then a jet of air from the wind snaps it back, giving you a really high reading.

I've also had the opposite affect where the rains passed and the sky cleared, but got a .01 reading every hour or so. Turns out pollen had formed a plug in the rain bucket cone and the water slowly seeped through causing the slow readings. My bucket now had a stainless steel screen to prevent such problems.

[Ptarmigan]

Thats per hour which means the bucket would need to dump 64 times in one hour. I would have picked up .60 per minute. With the instaneous flooding of roads and fields its possible. However I will continue to investigate this reading. I had another discussion on the channel 11 board.

Did anyone else recieve extremely high rainfall rates during the severe storm?

Wow! .6 inches per minute is very intense.

[KatDaddy]

I did a quick check the other day on the VP2 weather station the tip bucket is completely enclosed. I just got the following response from Davis this morning.

Hello,

Usually the wind does not effect the buckets because they are enclosed. Although I'm not saying this could not happen but I think it is unlikely.

That was just the maximum rainfall rate so a a particular time it could have been raining that hard.

[KatDaddy]

Thread name change suggested. Severe Storms and Heavy Rain Late Next Week

FROM HPC DISCO FRI. We are saturated and cannot handle another excessive rain event late next week

...WITH MOST ACTION
FOCUSING OUT FROM THE WRN AND ESPECIALLY SWRN US INTO THE
S-CENTRAL US AND UP THRU THE E-CENTRAL US FROM THE MIDDLE THRU
LATER PART OF NEXT WEEK. THIS OCCURS AS MID-UPPER LEVEL ENERGY
EDGES EWD AND TAPS WIDE OPEN GULF OF MEX RETURN FLOW ON THE WRN
PERIPHERY OF THE BUILDING E-CENTRAL US RIDGE AND ULTIMATELY
RUNS/TRAINS INTO/ALONG SLOW MOVING FRONTAL ZONES AND ANY MESO
BOUNDARIES...LEADING TO A THREAT OF A LOCALLY EXCESSIVE RAINS AND
HEAVY CONVECTION.

[Extremeweatherguy]

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
349 PM CDT FRI MAR 16 2007

.DISCUSSION...
HIGH PRESSURE WILL BE BUILDING ACROSS SE TX TONIGHT BEHIND THE
FRONT THAT WAS NOW OFF THE COAST. THE MODELS LOOKED SIMILAR IN
BRINGING THE RETURN FLOW BACK OVER THE AREA BY LATE SATURDAY. THE
MAIN ISSUE FOR THIS FORECAST CYCLE WILL BE THE RAIN CHANCES AND
TEMPERATURES NEXT WEEK.

THE ECMWF IS SLOWER THAN THE GFS WITH THE UPPER TROUGH THAT IS
EXPECTED TO MOVE ACROSS THE STATE IN THE MID TO LATE PART OF NEXT
WEEK. THE GFS ENSEMBLE MEMBERS LOOKED IN FAIR AGREEMENT UNTIL
ABOUT TUESDAY OR WEDNESDAY AND THEN INDICATED THAT THE MODEL MAY
BE TOO FAST WITH THE EASTWARD MOVEMENT OF THE TROUGH. DID NOTICE
THAT THE GFS ENSEMBLE QPF AND STANDARD DEVIATION INDICATED
ISOLATED RAINFALL POTENTIAL BEGINNING TUESDAY WITH BETTER CHANCES
LATE TUESDAY NIGHT IN THE NORTH AND OVER ALL OF SE TX WEDNESDAY.
THE BEST RAIN CHANCES LOOK TO BE THURSDAY AND FRIDAY...HOWEVER
WILL CONTINUE THE CHANCE POPS GIVEN THE TIME PERIOD. IF THE SET UP
MIRRORS THIS PAST WEEK...STRONG THUNDERSTORMS CANNOT BE RULED
OUT...AND WILL REISSUE THE HAZARDOUS WEATHER OUTLOOK TO BEGIN
MENTION OF THUNDERSTORMS FOR WEDNESDAY AND THURSDAY.

WITH GOOD WARM AIR ADVECTION AND MOISTURE ADVECTION OFF OF THE
GULF OF MEXICO NEXT WEEK...DECIDED TO UP THE MINIMUM TEMPERATURES.
WILL ALSO SEE MID 70S DURING THE DAYTIME PERIODS.

Late next week may certainly wind up being interesting yet again...

BTW: KatDaddy, I agree. We do not need another heavy event after last week. I recieved a good 4-4.5" of rain between Monday and Wednesday of last week, and another similar total would likely lead to even worse flooding concerns (since the ground is already saturated). Also, throw in a high wind-packing thunderstorm or two over the saturated soil, and we could have serious tree issues as well (with them being more vulnarable to uprooting).

[Yankeegirl]

It wasnt supposed to rain today, but we got a pretty good downpour this afternoon... Go Figure!!

[hurrican19]

It wasnt supposed to rain today, but we got a pretty good downpour this afternoon... Go Figure!!

That's when you got to be careful! Pretty much, anytime in SETX that they predict a -0%- chance of rain, is when it rains

[Ptarmigan]

That's when you got to be careful! Pretty much, anytime in SETX that they predict a -0%- chance of rain, is when it rains

Tell me about it! I remember it was a clear night and suddenly I heard thunder and it started to rain and it was at night, a summer night.

[Extremeweatherguy]

Here's a question..is one of these forecast offices wrong? or if not, how is it going to be so much windier in Waco today than in Houston (if the direction in both places is out of the south)?

Waco's forecast:

Today: Mostly cloudy, with a high near 76. Windy, with a south wind between 20 and 25 mph, with gusts as high as 35 mph.

Houston's forecast:

Today: Partly cloudy, with a high near 76. South wind between 15 and 20 mph, with gusts as high as 20 mph.

That is a pretty significant difference isn't it?

I mean I would expect this in a situation where a front was coming in, or there was a strong low pressure area in north Texas, but I would not expect such a difference during a day like today.

UPDATE: So far the forecast seems pretty accurate. Waco has indeed seen gusts to 30mph+ today, yet Houston has not.

[vbhoutex]

Here's a question..is one of these forecast offices wrong? or if not, how is it going to be so much windier in Waco today than in Houston (if the direction in both places is out of the south)?

Waco's forecast:

Today: Mostly cloudy, with a high near 76. Windy, with a south wind between 20 and 25 mph, with gusts as high as 35 mph.

Houston's forecast:

Today: Partly cloudy, with a high near 76. South wind between 15 and 20 mph, with gusts as high as 20 mph.

That is a pretty significant difference isn't it?

I mean I would expect this in a situation where a front was coming in, or there was a strong low pressure area in north Texas, but I would not expect such a difference during a day like today.

UPDATE: So far the forecast seems pretty accurate. Waco has indeed seen gusts to 30mph+ today, yet Houston has not.

Without looking at anything, my guess would be that Waco is simply closer to the "center"(whatever and wherever it may be)and has another system elsewhere closer to Waco which is enhancing the pressure gradient between the two systems and therefore giving Waco higher winds.

[PTrackerLA]

Models have backed WAY off of the system for the weekend. The 12Z GFS barely shows us getting any precip until next Tuesday/Wednesday now.

[Extremeweatherguy]

Models have backed WAY off of the system for the weekend. The 12Z GFS barely shows us getting any precip until next Tuesday/Wednesday now.

yeah, I noticed that too. Pretty big swing in the models compared to a few days ago.

because of this, the newest NWS forecast for Houston only has 20% chances of rain this upcoming weekend.

[jasons2k]

Here's a question..is one of these forecast offices wrong? or if not, how is it going to be so much windier in Waco today than in Houston (if the direction in both places is out of the south)?

Waco's forecast:

Today: Mostly cloudy, with a high near 76. Windy, with a south wind between 20 and 25 mph, with gusts as high as 35 mph.

Houston's forecast:

Today: Partly cloudy, with a high near 76. South wind between 15 and 20 mph, with gusts as high as 20 mph.

That is a pretty significant difference isn't it?

I mean I would expect this in a situation where a front was coming in, or there was a strong low pressure area in north Texas, but I would not expect such a difference during a day like today.

UPDATE: So far the forecast seems pretty accurate. Waco has indeed seen gusts to 30mph+ today, yet Houston has not.

Without looking at anything, my guess would be that Waco is simply closer to the "center"(whatever and wherever it may be)and has another system elsewhere closer to Waco which is enhancing the pressure gradient between the two systems and therefore giving Waco higher winds.

Yes, right after I read this yesterday (haven't had a chance to be online since) - I saw the Channel 11 or 13 noon news in our deli downstairs and they showed a front up in OK with a low pressure center out in West Texas. The met commented that the pressure gradient was tighter to our west and was resulting in quote "very gusty winds today out in Central Texas." Also, Waco and points west of there are out in the plains, with less trees and natural wind breakers, so it's more windy out there regardless of system placement. Just compare a wind rose between Houston and Lubbock sometime...