Scientific Forecaster Discussion
fxus64 khun 060432
Area forecast discussion
National Weather Service Huntsville Alabama
1032 PM CST Thu Dec 5 2019
for 06z tafs.
issued at 800 PM CST Thu Dec 5 2019
Some light reflectivity returns seen on radar as of 02z are
currently moving eastward across southern Tennessee and northern Alabama may
result in some isolated sprinkles this evening, but given dry airmass
in place not expecting measurable rainfall. Both bmx and ohx 00z
upper air soundings show Stout dry airmass up to around 3 km, hence
left dry forecast overnight as it will take some time to saturate the
lower levels. Otherwise, clouds continue to stream in from the west
overnight ahead of the next shortwave to the west. As a result,
temperatures remain mild overnight in the mid 40s across the
Short term...(friday through saturday)
issued at 254 PM CST Thu Dec 5 2019
An approaching shortwave trough will cause increased cloud cover and
rain showers to move into the area beginning in the late morning
hours of Friday and continuing through the evening. Expected
accumulated precipitation amounts between a 0.25" and 0.5".
Temperatures will peak at the lower 50s in the late afternoon. As the
rain subsides and the high pressure system moves northward off the
coasts of the Carolinas Friday evening, the wind direction will shift
from southeast to a more easterly flow. Temperatures expected to fall into
the mid 40s overnight as cloudy conditions linger into Saturday
morning. A surface high will build in for Saturday, with tranquil
conditions expected. However, lingering moisture in the lower
atmosphere will result in broken decks of cloud cover through the
day. Still, enough breaks will exist to allow US to warm to near
seasonable levels in the mid to upper 50s.
Long term...(saturday night through wednesday)
issued at 254 PM CST Thu Dec 5 2019
The ridge of high pressure over the Ohio Valley will shift into the
mid-Atlantic region, inducing a southerly return flow over the
Tennessee Valley region on Sunday. This will result in a brief
warming trend as temperatures jump back into the upper 50s. Other
than some scattered to broken decks of clouds, it should be a dry
and fairly pleasant day with at least some peaks of sunshine. The
next storm system will begin to take shape across the Southern Plains
Sunday night and lifts NE into the Ohio Valley on Monday. An
increasing southerly flow off the Gulf of Mexico will result in
strong warm air advection as temperatures surge into the mid 60s
along with good moisture return (dewpoints in the 50s). With the
front still to the northwest of the area and only weak lift in place,
expect Monday to be mainly dry with perhaps some scattered light
showers that will increase, especially in the afternoon.
The aforementioned cold front will Sage into the region Monday night.
As the best combination of lift and moisture are maximized during the
00-12z Tuesday time period, we expect a period of moderate to heavy
rain showers (with a few isolated thunderstorms) Monday evening
through early Tuesday morning. There will be a few environmental
factors that will support a threat for heavy rainfall and possibly
some localized flooding during this period -- namely high precipitable water
values around 1.5", combined with deep southwesterly flow parallel to
the frontal boundary. This, combined with some elevated cape), should
result in the potential for some training convection and thus an area
of enhanced precipitation over portions of the region. The latest
quantitative precipitation forecast estimates for this period indicate between 1.5" to 2.25" of
rainfall is possible which at the very least could be enough to get
some of the Tennessee River tributaries to respond. We'll have to
keep a close eye on this on the coming days as models have been in
pretty good agreement about the timing of this system.
Thereafter, expect a significant cool down for Wednesday as a strong
Canadian high pressure system builds south into the Tennessee Valley.
This will result in highs in the 40s and lows back below the freezing
mark once again.
Aviation...(for the 06z tafs through 06z Friday night)
issued at 1032 PM CST Thu Dec 5 2019
High clouds continue to stream in from the west ahead of the next
shortwave to reach our area by morning. Some virga from earlier
across southern Tennessee has produced some lower end VFR cigs, but they
should remain away from terminal overnight. Rain begins over western
Alabama after sunrise which in turns lowers cigs throughout the morning.
Kept out IFR cigs at this time, but potential does exist around
midday tomorrow especially if heavy showers occur.