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Area forecast discussion 
National Weather Service Tallahassee Florida 
300 am EST Thursday Jan 8 2009 


Synopsis...04 UTC surface analysis shows a 980 mb surface low over 
eastern New England with the cold front extending across the western 
Atlantic and into the Florida Straits. A weak surface trough was 
analyzed across the Ohio River valley heading into the southern 
Appalachians. A weak area of high pressure was noted southeast of 
the mouth of the Mississippi River. A very cold and dry airmass was 
across the upper Midwest with temperatures solidly below zero and 
dewpoints as low as -20f. 


Upper air data from 00 UTC continued to show the deep trough 
progressing across the eastern half of the country with ridging 
moving into the western U.S. 


&& 


Short term...today through Saturday. 
The weak surface trough will move through the southern Appalachians 
and across our region this afternoon and evening. This will tighten 
the pressure gradient and create another day with breezy 
winds...albeit nowhere near as strong as those seen on Wednesday. 
Model soundings also show 30 to 35 knot winds at 900 mb at all 
inland sites. Since we will easily mix to this height...some of 
these stronger winds will be transported down to the surface in the 
afternoon. It is looking like sustained winds in the 15 to 20 miles per hour 
range with gusts up to 30 miles per hour will be a good bet in the afternoon. 
With the passing of the upper trough across our region we'll have some 
mainly higher level clouds stream overhead...but these should be 
relatively transparent...so a partly cloudy/mostly clear day is 
expected with temperatures still hovering around the 70 degree mark. 


As a cooler area of high pressure moves southward toward our region 
Thursday night...temperatures Friday morning and into Saturday will 
return to near normal values in the morning. Afternoon temperatures 
will be slightly above normal...but still cool compared to what 
we've seen in the last couple of weeks. 


With a quick progressive pattern across the eastern Continental U.S....the 
ridge of high pressure will shift east on Saturday as a storm system 
approaches from the west. A cold front will move across the 
southeast Saturday afternoon and into the evening hours bringing 
increasing chances for showers and thunderstorms. There has been a 
little better agreement this cycle between the models for this time 
range of the forecast. The GFS still appears to be slightly faster 
than the NAM and Euro. Interestingly...the 07/21z sref mean fields 
are faster than even the GFS. With the associated upper trough 
becoming less amplified with time...would prefer a slightly slower 
solution indicated by the NAM as it just doesn't appear as though 
this front will roll through all that fast. As a result...the 
forecast is essentially a blend between the NAM and GFS solutions 
through 00z Sunday. 


Only a 12-18 hour period of decent return flow over the Gulf of 
Mexico is expected ahead of this storm system. Dewpoints over the 
northern Gulf have dropped into the middle and upper 40s behind 
yesterday's front. It will take some time for this airmass to 
recover and dewpoints in the 60s to get back into the northern Gulf. 
Thus...it is expected the airmass inland will be rather stable the 
further north you go. Models show dewpoints breaking into the lower 
60s by Saturday afternoon mainly in Florida. Over time...we've seen 
that the 60 degree dewpoint value is a critical threshold for the 
determination of a severe weather threat. Models are indicating at 
best 500 j/kg of SBCAPE ahead of the front...and with forecast 
lifted indices in the 0c to -1c range...the thermodynamic 
environment is looking rather weak. Kinematically...this system 
should be nearly as impressive as the Tuesday night system. Both the 
GFS and NAM have 0-6km bulk shear values in the 60 to 70 knot range 
across our region and an associated 45 to 55 knots 850 mb jet. Given 
that the instability with this system will be much like Tuesday 
night's storm system...will only mention isolated T in the forecast 
for now. 


Long term (saturday night through thursday). 
Although there is still quite a bit of uncertainty and lack of model 
run to run continuity in the extended period...confidence is still 
high that we will be in store for a generally cold and dry pattern 
for the majority of the period...as the mean upper level trough will 
remain entrenched over the eastern U.S.. exactly how cold will it 
get and which days will be the coldest is still somewhat in 
question...but would not be surprised to see at least a widespread 
light freeze on Wednesday and Thursday mornings. Will hold off on any hard 
freeze temperatures for at least another model cycle or two...until the 
timing and model consistency sufficiently improves. Also...after the 
1st in the series of cold fronts exits the area on Sunday morning 
(which the GFS and European model (ecmwf) are becoming increasingly in better 
agreement with time)...expect a virtually pop free forecast for the 
remainder of the period. 


&& 


Marine...winds over the coastal waters remain even below exercise 
caution criteria. However...seas at the buoys are still at 7 feet as 
of 2 am EST. It is expected that these seas will drop below 7 feet 
by 4 am...so the Small Craft Advisory over the offshore legs will be allowed to 
expire at that time. The remainder of the forecast in the first 2 
periods remains somewhat complicated. Winds may at times approach 20 
knots over the waters...or low end advisory criteria. However...seas 
are not expected to build back to 7 feet. Given that only 
intermittent bursts to 20 knots are expected this afternoon and 
early evening...will opt for an exercise caution headline across the 
board today and this evening before winds and seas diminish 
considerably after midnight. Winds and seas will build again on 
Saturday ahead of the approaching frontal system and will likely 
meet or exceed advisory criteria by afternoon. A prolonged period of 
advisory conditions looks good behind the cold front until Sunday 
evening. 


&& 


Aviation...much more benign taf package overnight tonight...with 
generally light west-SW winds and some scattered cirrus moving in from the west 
as the base of the upper level trough swings through the region. After 
sunrise...however...expect the west winds to quickly become gusty once 
again...and many of the taf sites may have a period of winds greater 
than 20 kts during the late morning and afternoon hours. This will 
likely be similar to...but not quite as strong...as the winds were 
on Wednesday afternoon. These winds should subside quickly after sunset as a 
surface ridge builds in from the northwest. 


&& 


Fire weather...with the dry airmass remaining over North Florida 
today...and winds at the surface above 15 miles per hour...will need to upgrade 
the inherited watch to a warning and likely expand it to include all 
of our counties. The secondary shot of dry air coming in tonight 
will lead to another potential round of red flag conditions on 
Friday in Florida...and potentially in a few counties in south 
central Georgia...especially along the Interstate 75 corridor. No 
red flag concerns are expected on Saturday as the front crosses the 
forecast area. Red flag conditions could return by Sunday if the 
front progresses quickly through the region. 


&& 


Preliminary point temps/pops... 
Tallahassee 71 40 67 40 74 / 0 0 0 0 40 
Panama City 71 45 66 54 72 / 0 0 0 0 50 
Dothan 66 38 66 48 70 / 0 0 0 05 60 
Albany 67 38 64 41 73 / 0 0 0 0 60 
Valdosta 69 39 66 39 75 / 0 0 0 0 30 
Cross City 72 40 69 41 74 / 0 0 0 0 20 


&& 


Tae watches/warnings/advisories... 
Alabama...Lake Wind Advisory from 10 am this morning to 5 PM CST this 
afternoon for the following zones: Coffee...Dale...Geneva... 
Henry...Houston. 


Georgia...Lake Wind Advisory from 11 am this morning to 6 PM EST this 
afternoon for the following zones: Baker...Ben Hill... 
Berrien...Brooks...Calhoun...Clay...Colquitt...Cook... 
Decatur...Dougherty...early...Grady...Irwin...Lanier... 
Lee...Lowndes...Miller...Mitchell...Quitman...Randolph... 
Seminole...Terrell...Thomas...Tift...Turner...Worth. 


Florida...Lake Wind Advisory from 11 am EST /10 am CST/ this morning to 6 
PM EST /5 PM CST/ this afternoon for the following zones: 
Bay...Calhoun...coastal Walton...Dixie...Franklin... 
Gadsden...Gulf...Holmes...inland Walton...Jackson... 
Jefferson...Lafayette...Leon...Liberty...Madison...Taylor... 
Wakulla...Washington. 


Fire Weather Watch Friday afternoon for the following zones: 
Bay...Calhoun...coastal Walton...Dixie...Franklin... 
Gadsden...Gulf...Holmes...inland Walton...Jackson... 
Jefferson...Lafayette...Leon...Liberty...Madison...Taylor... 
Wakulla...Washington. 


Red flag warning from noon EST /11 am CST/ today to 5 PM EST /4 
PM CST/ this afternoon for the following zones: Bay... 
Calhoun...coastal Walton...Dixie...Franklin...Gadsden... 
Gulf...Holmes...inland Walton...Jackson...Jefferson... 
Lafayette...Leon...Liberty...Madison...Taylor...Wakulla... 
Washington. 


GM...none. 


&& 


$$ 


Long term/aviation/fire weather...Gould 
rest of discussion...Godsey 

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