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Dothan Area Weather Forecast Sep 21

Wet weather pattern (of some duration) to begin later today...

NEAR TERM [TODAY]...

The tranquil pattern of recent days will come to an end later today.

The large scale amplified pattern this morning is highlighted by
ridging over Wrn and Cntrl Conus, a trough over Ern Conus with
low in Canada north of Great Lakes and axis Swd into MS River Valley
and Wrn Gulf region, and a shortwave ridge over N FL/SRN GA. Ridge
slowing down progression of advancing upstream moisture. At
surface, low over Ontario with cold front SSW down TN Valley thru
weak low Nrn LA thru Cntrl TN and into SE TX. Showers and Tstms
were noted in MS/LA along and ahead of front . Surface ridge over
extreme Wrn Atlc SWWD to Ern FL. Low over Wrn Gulf of Mex south of
Brownsville TX was moving NNE.

During the rest of today, shortwave energy swinging through middle
of the sharp trough will continue to propagate it ESE across OH
Valley into AL before weakening and lifting NEWD this eve. This
shunts ridge into Atlc.

At surface, the area of high pressure will progressively erode as the cold front slides EWD extending across NE GA, SE AL and into Gulf waters by sundown. A deep plume of moisture surging northward from the Gulf ahead of this front will progressively overspread local region from SW-NE. This reflected in model soundings i.e. RAP13 with 12z DHN showing 1.58 PWAT with significant low level veering then WLY flow above H7 increasing at 20z to 2.13 PWAT with SW flow up to H5 with SW flow up to H5. TLH increases from 1.64 to 1.97 inches PWAT same time.

At this point, with ridge into Atlc, and trough lifting newd, base of trough over Gulf region begins to flatten while at low levels the combination of a wave or mesolow developing on front over Cntrl AL/GA border and the Nwd movement of remnants of Gulf low begin to retard progress of Swd tail of front increasing rain chances and locally heavy rain potential late. 00Z GFS has best handle how far south trough will dig, and with timing of front.

These sounding profiles which show weak instability/lapse rates argue against severe weather outside of the potential for nuisance
flooding. However cannot discount strong to possibly isold severe
storms later this afternoon before the cloud cover overspreads the
region. Best shot will be just south of surface low along front
progged to be in N/Cntrl AL then GA this aftn then eve, especially
if low deepens. This would impact mainly our Nrn tier counties.
Jackson MS reported 2 brief spinups just south of low with 30-40kt
Low level jet axis during predawn hours so it bears watching.

Will go with sharp NW-SE POP gradients, 50-20% this morning
increasing to 70-30% in the afternoon. This reflected will in all the CAM and in all HI RES guidance although WRF faster in timing.
HRRR doesnt have more than isold rain to our wrn counties until near
midday.

Increasing clouds and rain will temper max temps into low to mid 80s west and mid to upper 80s east.

There is a high rip current risk for Bay and Walton Counties.

SHORT TERM [Tonight Through Monday]...

Extremely complex fcst over the short term period (but especially
beyond), and although our confidence is still quite high in a fairly wet and gloomy weekend with a slow moving cold frontal passage as an
upper shortwave traverses the Gulf Coast, all bets are off for early
next week.

The last 2 runs of the GFS (with Upper Air data, 12 and 00 UTC) are showing a rapid drying scenario, and was hoping that the new 00 UTC ECMWF would trend this way. Well, it has not, but at least does show the cold front making further southward progress on Monday (which could result in lower PoPs to the north for a while).

In any event, did NOT bite off too far in either direction with this much uncertainty, so kept PoPs fairly close to our locally derived Confidence Grids, with a few upward adjustments, since the very low GFS derived PoPs (which have more related members to weight), influenced these grids downward.

So, while the fcst remains confident in high Pops through the weekend, from Monday through mid-week will be a bear of a fcst.

At least it now appears that any Tropical Cyclone threat in the Gulf of Mexico this week has virtually been eliminated.

LONG TERM [Monday Night through Friday]...

There is still considerable disagreement between the GFS and ECMWF with respect to how quickly deep layer ridging builds in from the west. However, the extended period will feature at least somewhat
of a drying trend, with temperatures near or slightly below average.

AVIATION [through 12 UTC Sunday]...

MVFR are still possible at area terminals thru 13Z this morning with
additional visibility restrictions at the Nrn terminals (DHN, ABY, VLD) for BR.

With a cold front approaching from our W, ECP and DHN are forecast to remain MVFR after sunrise. Will go with -RA transitioning to 6SM RA 18z-06z from NW-SE.

Scattered thunderstorm coverage ahead of the main front should start this afternoon, but exact timing/location is still uncertain, so kept it VCTS. With cold front stalling across local area tonight, expect prevailing MVFR CIGS/VSBYS with IFR conditions especially CIGS in any heavy rain or fog thru 12z Sunday.

MARINE...

Did make some important changes to the current forecast, partially
based on the new run of the GFS, but blended its stronger onshore
winds ahead of the front with the latest SREF.

This will result in higher winds and seas than the previous package, but the maximum result should be a period of Cautionary Conditions over the weekend, with a return to light winds and low seas thereafter.

However, with the new ECMWF run still quite a bit different, all winds and seas may need to be adjusted later today, as there is still just too much uncertainty in the Global Models.

However, the threat for mariners to encounter a potential Tropical System in the Gulf of Mexico this week HAS decreased to almost nil.

HYDROLOGY...

New estimated rainfall amounts through Monday are now generally in
the 1 to 3 inch range (lowest to the NE and highest to the SW) with
locally higher amounts still possible.

These totals should have little impact on area rivers which have had quite a bit of time to subside since the last heavy rainfall event.

However, it is the early to mid week period where the uncertainty lies, and if the GFS is correct, we will have no problems at all, but the if the ECMWF becomes the model of choice river flooding will still be on the
table.

FIRE WEATHER...

With a front lingering across the local area into the early work week, no fire weather concerns are expected through the foreseeable
future.

PRELIMINARY POINT TEMPS/POPS...

Tallahassee 87 72 85 69 87 / 60 50 50 30 50
Panama City 84 73 84 73 85 / 70 60 60 30 50
Dothan 83 68 85 66 85 / 70 70 30 20 40
Albany 86 69 83 67 83 / 60 60 40 20 40
Valdosta 88 70 84 68 86 / 40 40 50 30 40
Cross City 87 70 83 69 88 / 30 30 60 40 50
Apalachicola 84 75 83 73 85 / 60 60 60 40 50

TAE WATCHES/WARNINGS/ADVISORIES...

FL...None.
GA...None.
AL...None.
GM...None.


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