Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 200001 AAA

Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
701 PM CDT Thu Apr 19 2018

For 00Z TAFS.


.NEAR TERM...(Tonight)
Issued at 241 PM CDT Thu Apr 19 2018

Area of stratocumulus is eroding quickly due to subsidence in wake of
departing upper shortwave and deep mixing. Gusts of 15-21kt are being
reported with temperatures warming into the lower to middle 50s in
north AL and upper 40s in southern TN. High pressure centered over
southern MN will drift east into WI tonight, with a rather stout
pressure gradient remaining around it`s circulation, including the TN
valley. This should maintain a 5-10kt flow most of tonight, thus temp
expectations are for mid-upper 30s for lows very late tonight. So
despite T-Td spreads of 2-4 degrees, frost should remain quite patchy
tonight, mainly in southern TN and parts of north AL.

.SHORT TERM...(Friday through Saturday night)
Issued at 241 PM CDT Thu Apr 19 2018

On Friday, as the surface high shifts east and upper ridging shifts
into the Ozarks and central Gulf Coast, dry east-southeast flow will
develop over the TN valley. Warm advection will be rather neutral at
best Friday, but as the column/thicknesses enlarge due to ridging and
stronger solar heating, temps should warm into the mid to upper 60s.

On Saturday, the ridge will shift into the OH valley to the southeast
Coast with broad southwesterly flow aloft developing. This will
enable moisture advection to increase and modest warm advection.
Mid and high clouds will likely increase by Saturday evening.
Increasing diffluence aloft develops quickly Saturday night as a
series of shortwaves ejects from the main upper trough moving out of
the Plains. The resulting combination of theta-e advection in low to
mid levels and good UVVs should enable showers to become scattered
to numerous rather quickly late Saturday night, especially in
northwest AL into southern middle TN.

.LONG TERM...(Saturday night through Wednesday)
Issued at 241 PM CDT Thu Apr 19 2018

Looks like another weekend will end on a soggy note across the TN
Valley. At least temps won`t be too bad, highs in the lower 60s (~10
degrees below normal), and lows in the lower 50s (normal values).

A cutoff upper-level low will weaken and slow down as it moves out
of the Southern Plains. An upper-level jet streak on the back side of
the low will put us in a diffluent pattern and the left exit region
of the jet. With the sfc low remaining to our south, this will be the
primary source of lift. Light rain will start Saturday night, but
soundings will saturate pretty quick by Sunday morning as a
southeasterly LLJ ~40-50kts moves in with PWATS reaching ~1.2". Lift
will be further enhanced on Sunday with WAA. All of this will lead to
rainfall will becoming widespread and heavier Sunday and Sunday
night. The upper-level low will make slow eastward progression and
continue to weaken on Monday due to an upper-level ridge along the
southeast Atlantic coast. Temps will be a near reflection of Sunday,
but POP chances will slowly decrease through the day leaving most
with scattered showers by Monday night.

By Tuesday, a strong shortwave moving into the Northern Plains will
give this upper-level low the push it needed to lift northeast.
However, it doesn`t get far before it becomes embedded within the
flow around the shortwave approaching from the northwest. It will not
be as breezy on Tuesday as it will be on Sunday and Monday since the
pressure gradient will be more relaxed, however scattered showers
remain in the forecast. There is still some model discrepancy about
the evolution of the shortwave, if it will be an open or closed low,
but none the less it looks like the system will bring a cold front
into the area on Wed, keeping rain chances lingering through mid-


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 702 PM CDT Thu Apr 19 2018

VFR conditions will prevail through the period with high pressure
established at the surface. Gusty winds will subside after sunset,
but a light northerly flow around 5-6 kts will persist overnight. A
clear sky will prevail through the end of the period.





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