Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 210156 AAB

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
856 PM CDT Fri Apr 20 2018

.NEAR TERM...(Tonight)
Issued at 856 PM CDT Fri Apr 20 2018

Quiet weather across the Tennessee Valley this evening, with high
pressure continuing to promote a clear sky and dry air mass.
Temperatures have dropped into the mid to upper 50s as of 02z, with
the loss of heating. The lack of cloud cover and a boundary layer
conducive for radiational cooling (dewpoints in the upper 30s) should
allow temperatures to fall into the low to mid 40s by the predawn
hours early Saturday morning. A dewpoint of 30 degrees at Ft Payne
was observed last hour, which could allow lows to drop into the upper
30s in sheltered valley areas of Northeast Alabama. Have showed this
cooler trend across portions of Jackson/DeKalb Counties in the
forecast grids, along with a light easterly flow gradually veering to
the ESE/SE around 3-5 kts after midnight. This light breeze, along
with the dry air within the boundary layer should prohibit any fog
development tonight. Very minimal changes needed based on current
obs/trends as the forecast remains on track.

.SHORT TERM...(Saturday through Sunday night)
Issued at 230 PM CDT Fri Apr 20 2018

Saturday will bring more sunny weather, with just some thin high
clouds entering the sky late in the day from the west. High
temperatures should easily reach the lower and possibly middle 70s
on Saturday afternoon.

The surface high will shift to the east coast with the 850 mb ridge
extending from the central Great Lakes into the Carolinas. This will
allow for a good fetch off the southwest Atlantic basin that will
help to increase dew points into the 40s to lower 50s by Saturday
night. This as the intense upper low/cold pool aloft over the
southwest U.S. reaches the southern Plains. The short range models
are in good agreement on an appreciable rain event for our area
Sunday into Sunday night. A highly diffluent mid and upper level
flow pattern will emerge over the lower MS and TN valleys by Sunday
morning. The column will be quick to saturate, especially over the
western half of our forecast area late Saturday night into Sunday
morning. Have continued an increasing chance of showers late Saturday
night, transitioning to categorical 90-100 percent range) as the
combination of strong dPVA/warm thermal advection produce a good
-divQ signal over the region. The QG forcing will combine with low
level flow veering to the south and an increasing Gulf moisture feed
to support widespread moderate to heavy showers. Mid level lapse
rates look to be more supportive of elevated convection embedded in
as well, so have included SCHC of embedded thunderstorms Sunday and
Sunday evening. Rain amounts will likely reach the 1-2 inch range
just in this period.

.LONG TERM...(Monday through Thursday)
Issued at 230 PM CDT Fri Apr 20 2018

Unsettled weather pattern for the work week ahead! The closed upper
low system expected to slide into the Southeast later this weekend
and bring heavy rainfall on Sunday will weaken and make very slow
eastward progression across the region on Monday and Tuesday. This is
due to an upper-level ridge along the southeast Atlantic coast.

Monday will have the best chance rain in the extended forecast. With
the sfc low remaining to our south pulling in more easterly flow,
losing lift as the upper-level jet sinks farther south, and the LLJ
lifting out of the area by late morning, will continue to keep
thunder out of the forecast with this system. Breezy conditions are
expected on Monday, especially in the morning with the LLJ across NE
AL and persist throughout the day with an increased pressure

Tuesday, a northern stream shortwave will swing into the Northern
Plains. This will have enough energy to push our southern stream
system NE starting Tuesday night. These two systems will phase
together Wednesday as the northern stream drags a cold front into the
area bringing an additional round of showers. There is model
disagreement on the timing and evolution of the phasing so kept with
lower POPs for mid-week.

The forecast will not have the warm up that you are hoping for,
however there are no low temps near freezing! Highs will linger
around the mid/upper 60s with lows in the upper 40s/lower 50s through
mid week.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 610 PM CDT Fri Apr 20 2018

VFR conditions will prevail through the period with fair weather
expected as high pressure remains in place. Winds will pick up to
around 10-12kts from the SE Saturday afternoon, with high clouds
increasing late in the day.





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