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Moderator: S2k Moderators
000
FXUS64 KCRP 161210
AFDCRP
Area Forecast Discussion
National Weather Service Corpus Christi TX
610 AM CST Sat Dec 16 2017
.DISCUSSION...
LONG TERM (Sunday night through Friday)...
Pattern remains active and there continues to be a hint of some
arctic air coming pretty far South toward the end of the forecast,
which if the moisture hangs around and there is enough forcing could
bring (if the airmass is dense enough) at least a brief bit of
winter weather (again) to the region (twice in less than a month
would be extremely unusual, especially during La Nina). However,
that is a ways out and normally the coldest of the models (Canadian)
is not showing this yet. However, at the very least it looks like
some cold air will get down here on Friday.
Before that, it still looks like the rain chances will continue over
the area especially Monday night and Tuesday as another upper trough
approaches the area. There will still be a chance for precipitation
Sunday night and Monday, mainly over the eastern portions of South
Texas (and gulf waters) as good moisture advection continues and
surface forcing is present. The upper trough moving toward the area
Monday night and Tuesday will allow a surface low and warm front to
develop Monday night, providing a focus for some convection.
Although most of the rain will be showers, there will be enough of
instability to provide for at least a slight chance for thunder,
with the better chance Tuesday over the eastern areas as daytime
heating erodes the cap along with the upper level forcing. The upper
trough moves east Tuesday night (taking the surface low with it) and
a brief interlude of dry weather comes in on Wednesday and continues
into Thursday. However, the moisture comes back Thursday night as a
frontal boundary approaches the area. The ECMWF and GFS show a
pretty strong arctic airmass with the boundary although the upper
fetch is not the arctic express far to the south one would want to
see to feel more confident in this to occur. However, the fetch is
into Oklahoma and if the airmass is dense enough it could get rather
cold even in our area. For now, did not go as cold as the raw GFS
and ECMWF (or their bias-corrected counterparts), but did go colder
than the Superblend as per other offices. The upper trough remaining
to the west will provide for at least a small chance for rain Friday
through Saturday night, although by late Saturday the ECMWF and GFS
show significant differences in the 1000-500 mb moisture fields
which, given where the colder air is supposed to reside in the
surface and boundary layer, could dictate whether any wintry
precipitation will be possible. The long and the short of it is to
stay tuned
Late Week-Next Weekend:
Let’s start with forecast confidence is not high from Thursday into next weekend.
Upper air pattern over the US will undergo amplification with deep layer ridging building along the US west coast deep into NW Canada and even the arctic circle. This will dislodge a cold arctic air mass and send it southward into the US by the middle of next week. Arctic boundary will arrive in TX on Thursday and likely cross SE TX early Friday. High temperatures will certainly be ahead of this boundary with rapidly falling temperatures Friday into the 40’s and eventually the upper 30’s (NW areas). The confidence in this arctic front making it off the coast sometime on Friday is fairly high along with a colder air mass moving into the region.
Next question then becomes how cold does the surface layer become. Arctic air masses tend to be very shallow in nature (sometimes only a feet thousand feet thick) with much warmer air above the surface cold dome. If moisture were to be in place for next weekend, the shallow nature of the cold air does NOT support snow or sleet. A shallow cold layer near the surface would tend to support freezing rain if and only if the surface temperature is at or below freezing…33 means a very cold rain and 31 would mean freezing rain. At this time the incoming air mass does not appear, at least initially, to be cold enough at the surface to result in freezing rain over much of SE TX. Freezing line may end up over portions of the I-35 corridor by Friday evening (22nd) and a bit southward by the morning of the 23rd. There is very little room for wet bulb cooling of the air mass since model cross sections show a fairly saturated air column over much of the state and surface temperatures and dewpoints are fairly close.
While the surface temperatures are one issue, the other issue is the handling of an upper level low which may dig into the SW US and how much moisture it will bring up and over the surface cold dome. While early, there is some degree of confidence that this upper level feature will form over the SW US by late week and provide a good amount of moisture over the state.
As with any winter weather event in TX, confidence is low as many times such events hinge on 1-2 degree differences in the temperatures which 5-6 days out is impossible to forecast. Run to run model variability continues to be poor which does not lend much confidence in any particular solution actually happening
Key Messages:
1) Significantly colder air mass will likely arrive next Friday and last through the holiday weekend
2) It is too early to determine how cold the air mass will be or if any freezing precipitation will occur over any portions of SE TX
3) Residents traveling to central and N TX late next week/weekend should monitor forecasts closely
Ralph's Weather wrote:missygirl810 wrote:Ok, dumb question, but going to ask anyway, is Hunt Co considered North TX or Northeast Tx, or Central TX? I have heard all three for my area lol
I would say Hunt Co would be N TX but very near the line with NE TX. For me, N TX is basically Abilene (maybe down to Brownwood) to Wichita Falls east to Athens and Paris. NE TX is east of Paris to Canton and north of I20. E TX is Paris to Buffalo and east to Texarkana to Jasper.
spencer817 wrote:Is anyone else thinking the GFS is too warm for DFW?
Cpv17 wrote:spencer817 wrote:Is anyone else thinking the GFS is too warm for DFW?
The GFS operational, yes. The GFS ensemble mean, no. It’s too bad most of the forecasters only go by the operational runs through.
Cpv17 wrote:spencer817 wrote:Is anyone else thinking the GFS is too warm for DFW?
The GFS operational, yes. The GFS ensemble mean, no. It’s too bad most of the forecasters only go by the operational runs though.
spencer817 wrote:It seriously boggles my mind as to why it avoids DFW on this run and many others.
Ntxw wrote:spencer817 wrote:It seriously boggles my mind as to why it avoids DFW on this run and many others.
12z GFS is a pretty close run for DFW, it's all a matter of temps as the precip shield is still fairly robust
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