Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/25/20
Area Forecast Discussion
National Weather Service Key West FL
1050 PM EDT Sat Oct 24 2020
The concern for heavy rain over the Keys has lessened over the
course of this evening. The warm front-like boundary that was
initially expected to hang up and focus heavy precip near the
Keys has now moved north of the Keys instead. Though we had a band
of transient showers move north across the Keys this evening, it
failed to linger long enough over the Keys to bring heavy rain,
except for radar-indicated amounts in excess of 1 inch near
Tavernier. Each successive run of the HRRR this evening has
lowered QPF for the rest of tonight. Have therefore updated the
forecast to remove the mention of heavy rainfall and to lower QPF
over the Keys through Sunday morning.
Tropical Depression 28 formed over the northwest Caribbean late
this afternoon. It is currently centered about 400 miles south of
Key West. It will move north-northwest and pass through or near the
Yucatan Channel around Monday. This path is very comfortably far
southwest and west of the Keys, so we will experience no adverse
impacts. However, the air mass remains extremely moist for late
October, with a PW value of a whopping 2.33" in the evening KEY
balloon sounding. Low-level southeast flow on the periphery of TD
28 will continue to reinforce the extremely moist air mass and
rounds of showers through about Monday, with some southwest shear
across the tropical cyclone streaming mid-upper level moisture
across the forecast area.
After Monday, the tropical cyclone will move further away from the
Keys as it move north through the Gulf, taking much of the
moisture with it. More modest levels of moisture currently out
east of the Bahamas will trickle in on Mon night and Tue.
At 8 pm EDT, the center of Tropical Depression 28 was located
about 400 miles south of Key West. It was moving slowly to the
north-northwest and will move northwest through the Yucatan
Channel around Monday. On this track, the Keys will mainly
experience fresh to strong southeast breezes through Monday. Then
an Atlantic ridge axis will build westward across the Florida
Peninsula from Tuesday through Thursday, bringing an easing of
Scattered showers and isolated thunderstorms will affect the Florida
Keys tonight and tomorrow as Tropical Depression 28 moves slowly
toward the SE Gulf of Mexico. MVFR cigs and IFR vis can be expected
with the passing squalls and wind gusts to 25 knots in the stronger
cells. Winds SE at 10 to 15 knots with occasional gusts to 20
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Area Forecast Discussion
National Weather Service Memphis TN
932 PM CDT Sat Oct 24 2020
Another chilly night ahead of us. Cold and cloudy is the main
story for tonight into tomorrow. Lows tonight will generally be in
the lower 50s. Latest radar imagery shows light returns,
indicating some drizzle might still be present in the Mid-South.
No real changes were made to the forecast.
PREV DISCUSSION... /issued 332 PM CDT Sat Oct 24 2020/
What a difference 24 hours makes? Temperatures are running nearly
35 degrees cooler across the area, in the wake of a cold front.
Heavy cloud cover and drizzle have been commonplace across the
area for much of the day. Aloft, an exiting shortwave can be seen
on GOES Water Vapor Imagery, with nearly zonal flow across the
belt of the Central U.S. Latest KNQA radar sweep reveals light
reflectivity returns, suggesting light precipitation and drizzle
across the area. The latest AMDAR soundings show a pronounced
elevated inversion across the region, which will keep this low
level moisture locked in through at least tomorrow.
Short term...Tonight through Tuesday...
Temperatures are expected to remain nearly steady overnight due to
drizzle and heavy cloud cover. Expect lows in the upper 40s to
lower 50s. Upper level flow will shift more southwesterly
tomorrow, as the upper low off the California coast comes ashore.
With heavy cloud cover nearly locked in place, temperatures will
not warm much. Expect highs to only reach into the low to mid 60s.
Expect dry conditions and slightly warmer temperatures to persist
Split flow over the West Coast will congeal into a large trough
by late Monday as it moves into the Desert Southwest Region.
Downstream of this feature, a cold front will drop down into the
Lower Mississippi Valley and stall over the northwest portion of
our CWA. This will keep low-end chances for rainfall in the
forecast for areas north of I-40 Monday night and Tuesday, with
mostly dry conditions to the south.
Long Term...Wednesday through next weekend.
The long term forecast has now been complicated by the genesis of
Tropical Depression 28 in the Caribbean. This system is now being
resolved in both synoptic models as potentially TS Zeta. Both
models bring the system up through Louisiana Wednesday into
Thursday. This will bring a surge of moisture north into the Mid-
South Wednesday ahead of an approaching surface low coming out of
the Southern Plains. The remnants of the tropical system and the
aforementioned surface low appear to merge as they move through
the region on Thursday. This will likely enhance lift and
convective coverage across the area, and produce generous amounts
of rainfall in its wake. For now, it appears the best chances for
rain will be Wednesday and Thursday, with up to 3 inches of
Behind the exiting system, dry northwest flow appears to set up
Friday through next weekend. This would translate to near normal
temperatures and mainly dry conditions.
Ceilings will remain near the IFR/MVFR threshold tonight, more
likely below this threshold east of the MS River. HRRR model
suggest the -DZ potential may expand to JBR, and increase at the
other TAF sites after 06z with a weak impulse wrapping around the
back side of the departing upper low.
Ceilings will be slow to lift Sunday, as modest surface heating
increases the depth of the mixed layer and the overlying thermal
inversion base. JBR should see flight conditions improve soonest
on Sunday, TUP the latest.
Area Forecast Discussion
National Weather Service Nashville TN
804 PM CDT Sat Oct 24 2020
FOR EVENING DISCUSSION.
Certifiably yucky evening across Middle Tennessee as WAA
continues above the shallow colder air at the surface as shown on
our 00Z sounding. Surface obs indicate cloudy skies and patchy
fog throughout the area, while radar shows scattered light
showers and drizzle mainly across the northern two-thirds. HRRR
and CONSShort show light showers will continue this evening but
gradually lift out to the northeast overnight, leaving mainly
patchy drizzle throughout the area. Have adjusted pops quite a
bit, especially over northern zones, based on this thinking and
latest radar trends. Temperatures currently range from the upper
40s in the northwest to the mid 50s in the southeast, and they
will remain steady or only slightly drop overnight due to
continued CAA from the north. Made some minor adjustments to
temps for tonight but nothing too notable.
00Z TAF DISCUSSION.
Poor flying conditions at all terminals now through the overnight
hours. BNA/MQY will remain with IFR cigs through the evening. CKV
will continue to see periods of -DZRA/-RA through 03Z with cigs
remaining along the MVFR/IFR thresholds. BNA/MQY/CKV could have
periods of LIFR cigs early tomorrow morning as well as periods of
CSV will remain with LIFR conditions through at least the early
morning hours tomorrow. Expect fog to develop overnight along
with continuing very low ceilings.
Ceilings will slowly begin to improve to MVFR at all terminals in
the mid-morning to early afternoon hours. Winds will remain light
and predominantly from the north through the TAF period.
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