Area Forecast Discussion
Issued by NWS Huntsville, AL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS64 KHUN 190233
AFDHUN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HUNTSVILLE AL
933 PM CDT SAT APR 18 2015

.UPDATE...
MADE SOME MINOR WORDING CHANGES...OTHERWISE CURRENT FCST LOOKS ON
TRACK.

&&

.DISCUSSION...
DEWPOINTS ACROSS NRN AL WERE MAINLY IN THE LOWER 60S COMPARED TO
ARND 70 OVER SRN AL. ALSO RADARS WERE SHOWING HEAVIER RAIN AND A FEW
STORMS MOVING INTO CENTRAL AL...ASSOCIATED WITH THE WARM FRONT. ATTM
ONLY SOME LIGHT SHRA WERE NOTED ACROSS THE TN VALLEY. HOWEVER THE
HRRR ALONG WITH THE NAM WAS SHOWING THAT THE HEAVIER RAIN WILL MOVE
INTO THE TN VALLEY ARND 09Z. NOT EXPECTING ANY SVR WX OVERNIGHT
BUT ANY STORMS THAT WOULD DEVELOP COULD PRODUCE WIND GUSTS UP TO 40
MPH ALONG WITH SMALL HAIL AND LOCALIZED HVY RAIN.

THUS DID NOT MAKE ANY MAJOR CHANGES TO THE FCST. UPDATED FCST/GRIDS
ALREADY SENT.

07

&&

.AVIATION...
/ISSUED 650 PM CDT SAT APR 18 2015/
FOR 00Z TAFS...A WARM FRONT OVER CENTRAL AL WILL CONTINUE TO MOVE
NORTH OVERNIGHT. THIS WILL INCREASE THE CHC OF SHRA AND A FEW TSRA
OVER THE TAF SITES BEGINNING ARND 02Z. SINCE INSTABILITY WILL BE
FAIRLY WEAK TONIGHT WILL KEEP PCPN AS ALL SHRA. FOR SUNDAY MAY HAVE A
BREAK IN THE PCPN BEGINNING ARND 18Z. HOWEVER WITH DAYTIME HEATING
AND THE APPROACH OF A CDFNT...COULD SEE SCT TSRA DEVELOP ACROSS THE
TAF SITE BETWEEN 20Z AND 24Z. OTHERWISE VFR CONDITIONS UNTIL
02Z AND THEN BETWEEN 02Z AND 12Z MAINLY MVFR. THERE IS A GOOD CHC OF
IFR CONDITIONS BETWEEN 12Z AND 18Z WITH MVFR CONDITIONS AFTER 18Z.

07

&&

.PREV DISCUSSION...
/ISSUED 417 PM CDT SAT APR 18 2015/

SCATTERED SHOWERS HAVE DEVELOPED ACROSS THE TENNESSEE VALLEY THIS
AFTERNOON MAINLY EAST OF INTERSTATE 65. THIS WAS IN RESPONSE TO
SLIGHTLY BETTER SURFACE HEATING. ACTIVITY IS NOT EXPECTED TO AMOUNT
TO MUCH WITH A CAP AROUND 500MB AND LIMITED CAPE AND WEAK FORCING.
SHOWERS SHOULD CONTINUE ACROSS NE ALABAMA THROUGH THIS EVENING UNTIL
BETTER FORCING ARRIVES INTO THE AREA.

TONIGHT...AN UPPER LEVEL DISTURBANCE IS FORECAST TO MOVE OUT OF THE S
TX/NORTHERN MEXICO AND INTO THE MS VALLEY OVERNIGHT. THIS WILL DRIVE
THE SURFACE LOW LOCATED OVER THE GULF AND ASSOCIATED WARM FRONT
THROUGH THE AREA OVERNIGHT. WHILE CAPE IS EXPECTED TO BE LIMITED AS
LAPSE RATES BECOME ALMOST COMPLETELY MOIST ADIABATIC OVERNIGHT...DEEP
LAYER SHEAR OF 40-50 KTS WILL DEVELOP OVER THE AREA. THE THREAT FOR
SEVERE THUNDERSTORMS WILL BE LOW TONIGHT. HOWEVER...THERE WILL BE A
NARROW WINDOW WHERE THE FORCING FROM THE WARM FRONT AND THE AVAILABLE
DEEP LAYER SHEAR MAY ALLOW FOR A FEW STRONGER THUNDERSTORMS TO
DEVELOP WITH WIND GUSTS UP TO 40 MPH AND SMALL HAIL POSSIBLE. SHOWER
AND THUNDERSTORM ACTIVITY SHOULD TAPER OFF TOWARDS SUNRISE SUNDAY
MORNING AS THE DISTURBANCE AND SURFACE LOW LIFT NORTH INTO THE OH
VALLEY.

SUNDAY AFTERNOON/EVENING...THE CLOSED UPPER LEVEL LOW THAT HAS BEEN
LOOMING OVER THE PLAINS STATES FINALLY BEGINS TO MOVE EAST SUNDAY.
VERY UNSTABLE CONDITIONS ARE EXPECTED TO DEVELOP SUNDAY AFTERNOON AND
EVENING WITH CAPE VALUES NEAR 2000 J/KG. THUNDERSTORM ACTIVITY MIGHT
BE LIMITED INITIALLY DUE TO WEAK FORCING AND WILL LIKELY BE TRIGGERED
OFF OF ANY LINGERING BOUNDARIES FROM MORNING SHOWER ACTIVITY.
HOWEVER...ANY STORMS THAT DO DEVELOP WILL LIKELY BE SEVERE WITH
DAMAGING WINDS AND LARGE HAIL POSSIBLE. BETTER FORCING IS NOT
EXPECTED TO ARRIVE UNTIL LATE SUNDAY NIGHT AS THE UPPER LOW MOVES
OVER THE AREA AND A COLD FRONT NEARS THE AREA. ACTIVITY WILL LIKELY
EVOLVE INTO A SQUALL LINE ALONG THE FRONT THAT WILL PUSH THROUGH LATE
SUNDAY NIGHT INTO MONDAY MORNING. DAMAGING WINDS...LARGE HAIL...AND A
BRIEF TORNADO WILL BE THE MAIN THREATS AS THE SQUALL LINE PUSHES EAST
ACROSS THE TENNESSEE VALLEY. THE FRONT SHOULD BE OUT OF THE AREA
MONDAY MORNING...HOWEVER LINGERING LIGHT SHOWERS WILL BE POSSIBLE
DURING THE MORNING HOURS AS THE MAIN UPPER LEVEL TROUGH AXIS ROTATES
THROUGH. ALL ACTIVITY SHOULD WIND DOWN BY MONDAY AFTERNOON WITH HIGH
PRESSURE BUILDING OVER THE AREA.

STUMPF

LONG TERM (TUESDAY THROUGH FRIDAY)...
VERY COOL AIR FOR THE MIDDLE TO END OF APRIL IS IN STORE FOR THE
EASTERN CONUS INCLUDING NORTHERN ALABAMA AND SOUTHERN MIDDLE TN...AS
850 MB TEMPERATURES DROP BEHIND THE FRONT TO BETWEEN 2 AND 5 DEGREES
CELSIUS IN NORTHERN ALABAMA. LONG TERM MODELS ARE VERY CONVERGENT ON
THIS SCENARIO AND THE ROBUST UPPER LOW WHICH ADVECTS MUCH COLDER AIR
INTO THE SOUTHEAST FROM CANADA. THE COLD AIR WILL MODIFY AS IT MOVES
INTO THE SOUTHEAST...BUT WILL BRING BELOW NORMAL TEMPERATURES TO THE
AREA. HIGHS ON TUESDAY WILL LIKELY STRUGGLE TO RISE INTO THE UPPER
60S IN THE WARMEST LOCATIONS. HIGHER ELEVATIONS OF SOUTHERN MIDDLE TN
AND NORTHEASTERN ALABAMA MAY NOT CLIMB ABOVE 65 DEGREES. ADJUSTED
GRIDS ACCORDINGLY. THIS MAY EVEN BE A BIT CONSERVATIVE. HIGH CLOUDS
WILL ALSO HELP TO LIMIT HEATING ON TUESDAY...AS A WEAK DISTURBANCE
MOVES THROUGH ZONAL FLOW OVER THE AREA.

SLIGHTLY NORTHWEST FLOW TO ZONAL FLOW WILL CONTINUE WITH THE BROAD
UPPER LOW SLOWLY PUSHING EAST INTO SOUTHEASTERN CANADA BY THURSDAY.
COLD AIR ASSOCIATED WITH NW FLOW AROUND THE UPPER LOW AND CLOUD
COVER/SCATTERED PRECIPITATION FROM DISTURBANCES PUSHING EAST BELOW
THE UPPER LOW WILL KEEP TEMPERATURES BELOW NORMAL. /NORMAL HIGHS ~75
AND NORMAL LOWS ~ 53/.

BY WEDNESDAY NIGHT...INCREASING MOISTURE CONVERGENCE ALONG A
BOUNDARY (DUE TO INCREASING RETURN FLOW FROM THE GULF OF MEXICO)
NEAR TENNESSEE BETWEEN THE EXITING UPPER LOW AND RIDGING TO THE
SOUTH...WILL COMBINE WITH ADDITIONAL DISTURBANCES TO PRODUCE PERIODS
OF SCATTERED SHOWERS AND STORMS THROUGH FRIDAY. FRIDAY NIGHT INTO
SATURDAY...A STRONGER DISTURBANCE ASSOCIATED WITH A SURFACE LOW
MOVING EAST OUT OF OKLAHOMA WILL POSSIBLY PRODUCE A MORE ORGANIZED
AND WIDESPREAD BATCH OF SHOWERS AND THUNDERSTORMS OVER THE AREA.
MODELS ARE FAIRLY DIVERGENT WITH THIS SCENARIO...SO JUST KEEPING THE
40 POP THAT WAS ALREADY IN THE FORECAST FOR THIS PERIOD.

KTW

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

FOR MORE INFORMATION PLEASE VISIT OUR WEBSITE
AT WEATHER.GOV/HUNTSVILLE.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.