National Weather Outlook
A storm system moving through the middle of the country will be responsible for a couple of days of heavy rain and strong to severe thunderstorm potential. Meanwhile, another storm system will into the Western U.S. with some additional moisture and high elevation snow.
Severe Threat Friday
…SUMMARY…
SEVERE THUNDERSTORMS ARE LIKELY THIS AFTERNOON INTO TONIGHT FROM THE
SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY. OTHER SEVERE
STORMS ARE EXPECTED OVER THE CENTRAL PLAINS. SUPERCELLS CAPABLE OF
LARGE HAIL…DAMAGING WINDS…AND PERHAPS A COUPLE STRONG TORNADOES
WILL BE POSSIBLE IN BOTH AREAS.
…SYNOPSIS…
PROGRESSIVE SPLIT-FLOW PATTERN WILL SOMEWHAT AMPLIFY THIS PERIOD AS
SRN BRANCH TROUGH NOW OVER N CNTRL MEX/SW NM CONTINUES NE TO THE ERN
TX PANHANDLE THIS EVE…AND INTO ERN KS EARLY SAT…WHILE UPSTREAM
NRN BRANCH TROUGH AMPLIFIES SE INTO CA. THE SHORTENING WAVELENGTH
ASSOCIATED WITH THIS PATTERN WILL TEMPORARILY STRENGTHEN THE NM
DISTURBANCE AND YIELD A BELT OF ENHANCED WSWLY FLOW OVER THE SRN
HALF OF THE PLNS LATER TODAY THROUGH TNGT.
AT LWR LVLS…EXPECT A SFC LOW TO CONSOLIDATE OVER THE OK PANHANDLE
BY THIS EVE…WITH THE LOW CONTINUING NE TO NEAR KANSAS CITY EARLY
SAT. IN RESPONSE…DIFFUSE WARM FRONT NOW EXTENDING ROUGHLY WNW-ESE
ACROSS WRN OK/N TX AND SRN LA WILL ADVANCE N/NEWD THROUGH THE
PERIOD. ITS POLEWARD NWD MOTION WILL…HOWEVER…LIKELY BE RETARDED
BY THE CONTINUING PRESENCE OF STORM CLUSTERS AND CLOUDS OVER ERN
PARTS OF THE SRN PLNS.
…SRN PLNS TO LWR MS VLY TODAY/TNGT…
SEVERE WEATHER SCENARIO WILL BE COMPLICATED IN THIS REGION BY
OUTFLOW FROM OVERNIGHT AND ONGOING STORM COMPLEXES…DIFFUSE NATURE
OF WARM FRONT…AND PRESENCE OF THICK MID/HIGH-LVL CLOUDS DOWNSTREAM
FROM NM UPR TROUGH. NEVERTHELESS…COMBINATION OF SFC HEATING AND
LOW-LVL UPLIFT ALONG OUTFLOW BOUNDARY ON SRN SIDE OF N TX CONVECTIVE
BAND…AND UPLIFT ALONG WARM FRONTAL SEGMENTS IN THE
VICINITY…SHOULD PROVE SUFFICIENT TO SUPPORT THE DEVELOPMENT OF
STRONG TO SVR STORMS BY MID TO LATE AFTN. THE ACTIVITY SHOULD BEGIN
IN CNTRL TX…WHERE INTERSECTION OF EWD-ACCELERATING DRY LINE WILL
ASSIST IN LIFTING PARCELS TO THE LFC. STORMS MAY THEN FORM AND/OR
INTENSIFY A BIT LATER EWD ALONG THE OUTFLOW BOUNDARY TOWARD THE
ARKLATEX. GIVEN 50+ KT WSWLY DEEP SHEAR ORIENTED ROUGHLY PARALLEL TO
THE OUTFLOW BOUNDARY/FRONT…AND RICH BOUNDARY LAYER MOISTURE /PW
AOA 1.75 INCHES/…POTENTIAL WILL EXIST FOR SUPERCELLS AND SUPERCELL
COMPLEXES WITH A RISK FOR VERY LARGE HAIL…HIGH WIND…AND
TORNADOES. GIVEN STRENGTHENING SWLY LOW-LVL FLOW ASSOCIATED WITH THE
EJECTING UPR TROUGH…THE STORMS LIKELY WILL MERGE INTO A FAIRLY
EXTENSIVE QLCS THIS EVE/TNGT. EMBEDDED SUPERCELLS WITHIN THIS
ACTIVITY COULD CONTAIN BOWS AND LEWPS POSING A CONTINUING SVR THREAT
EWD ACROSS SRN AR AND NRN/CNTRL LA INTO NRN/CNTRL MS EARLY SAT.
…CNTRL PLNS THIS AFTN INTO TNGT…
A SEPARATE SVR THREAT AREA LIKELY WILL EVOLVE OVER PARTS OF CNTRL
PLNS THIS AFTN AND EVE…WHERE SFC HEATING AND THE APPROACH OF THE
SRN BRANCH TROUGH WILL FURTHER DESTABILIZE REGION. SOME ASPECTS OF
THE SITUATION ARE CERTAINLY FAVORABLE FOR SUPERCELLS…ESPECIALLY
ALONG A ROUGHLY SW-NE DIAGONAL AXIS ACROSS CNTRL AND ERN KS. BUT THE
SFC LOW WILL REMAIN RATHER LOOSELY-ORGANIZED THROUGH THE DAY…AND
THE STRONGEST MID-UPR LVL FLOW WILL REMAIN S OF THE REGION. COUPLED
WITH THE PRESENCE OF ONLY MODEST MOISTURE RETURN DUE TO CONTINUING
PRESENCE OF STORMS FARTHER S…AND PERSISTENT CLOUD COVER…DEGREE
OF STORM COVERAGE AND INTENSITY IS UNCLEAR ATTM.
NEVERTHELESS…ESPECIALLY ACROSS PARTS OF KS…POCKETS OF ENHANCED
BUOYANCY/CONVERGENCE LIKELY WILL YIELD AT LEAST SOME STORMS CAPABLE
OF LARGE HAIL AND TORNADOES…IN ADDITION TO LOCALLY DMGG
WIND…INTO EARLY TNGT.
Severe Threat Saturday
…SUMMARY…
SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP DURING THE AFTERNOON
ACROSS PORTIONS OF THE LOWER OHIO VALLEY AND TENNESSEE VALLEY. VERY
LARGE HAIL…DAMAGING WINDS…AND TORNADOES ARE POSSIBLE.
ISOLATED SEVERE THUNDERSTORMS ARE ALSO POSSIBLE ACROSS MUCH OF THE
GULF COAST REGION.
…LOWER OH/TN VALLEY REGION…
BAJA PENINSULA SHORT-WAVE TROUGH WILL EJECT NEWD INTO THE CNTRL/SRN
PLAINS DURING THE LATTER HALF OF THE DAY1 PERIOD…THEN INTO THE MS
VALLEY BY DAYBREAK SATURDAY. STRONG MID-LEVEL SPEED MAX…ON THE
ORDER OF 80KT…IS FORECAST TO TRANSLATE ACROSS AR TO NEAR THE TN/AL
BORDER BY EARLY AFTERNOON. 12HR HEIGHT FALLS NEAR 90M SHOULD SPREAD
NORTH OF THE SPEED MAX ACROSS THE LOWER OH/TN VALLEY REGION WITH
FOCUSED CORRIDOR OF FORCING FOR ASCENT EXPECTED ALONG A WARM FRONT
THAT WILL DRAPE ITSELF FROM SRN IL…INTO ERN KY.
SUBSTANTIAL WLY DEEP LAYER FLOW IS EXPECTED TO DRAW A PLUME OF STEEP
LAPSE RATES/DRY SLOT EWD ACROSS THE PLAINS INTO SRN MO/AR REGION
EARLY IN THE PERIOD. BY MID-DAY A FAIRLY WELL-DEFINED DRY LINE
SHOULD EXTEND FROM A SFC LOW OVER CNTRL MO…SWD INTO AR. STRONG
HEATING EAST OF THE DRY LINE IS EXPECTED IN THE WAKE OF
EARLY-MORNING MCS THAT SHOULD BE DRIVEN BY WARM ADVECTION. AS A
RESULT…THERE IS INCREASING CONFIDENCE THAT SUBSTANTIAL WARM SECTOR
RECOVERY WILL BE NOTED WITHIN VEERED FLOW REGIME SUCH THAT MODERATE
BUOYANCY AND STRONGLY SHEARED PARAMETER FIELDS WILL BECOME
SUPPORTIVE OF DISCRETE SUPERCELLS. WHILE THE STRONGEST FORCING IS
EXPECTED ALONG THE WARM FRONT…IMMEDIATELY AHEAD OF SFC LOW AS IT
TRACKS ESEWD ALONG THE BOUNDARY…STORMS THAT DEVELOP JUST SOUTH OF
THE WARM FRONT ACROSS KY AND TN SHOULD EASILY ROTATE AND VERY LARGE
HAIL AND TORNADOES ARE EXPECTED. CONDITIONS COULD EVOLVE SUCH THAT
A FEW STRONG TORNADOES ARE POSSIBLE. WILL CONTINUE TO MONITOR THIS
REGION FOR POSSIBLE INCREASE IN SEVERE PROBABILITIES IN LATER
OUTLOOKS.
…GULF COAST REGION…
SEVERE THREAT SOUTH OF AFOREMENTIONED MID-LEVEL SPEED MAX WILL BE
MORE NEBULOUS ACROSS THE GULF COAST STATES. LATEST THINKING IS A
SUBSTANTIAL EARLY MORNING MCS WILL TRACK ACROSS THE NRN GULF
STATES/TN VALLEY REGION WITH A TRAILING SFC BOUNDARY DRAPED SWWD
ALONG THE TX COASTAL PLAIN. STRONGEST LOW-LEVEL HEATING/STEEPEST
LAPSE RATES WILL FOCUS NORTH OF THIS REGION BUT DEEP-LAYER SHEAR
WILL PROVE SUPPORTIVE OF ORGANIZED ROTATING UPDRAFTS. IT/S NOT REAL
CLEAR HOW CONVECTION WILL EVOLVE ACROSS THIS REGION BUT CONVECTIVE
INHIBITION IS EXPECTED TO BE SUFFICIENTLY WEAK FOR SCT THUNDERSTORMS
TO INCREASE DURING THE DAY…ESPECIALLY FROM THE UPPER TX COAST INTO
PORTIONS OF SRN GA. GREATEST RISK WILL BE DAMAGING WINDS AND
PERHAPS A FEW TORNADOES…AS LAPSE RATES ARE EXPECTED TO BE WEAKER
ACROSS THIS REGION THAN FARTHER NORTH.
Severe Threat Sunday
…SUMMARY…
SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS THE SOUTHERN
PLAINS SUNDAY AFTERNOON AND CONTINUE INTO THE EVENING HOURS.
ISOLATED STRONG STORMS MAY ALSO DEVELOP ACROSS THE REMAINDER OF THE
GULF COAST STATES.
…SOUTHERN PLAINS…
BOTH THE NAM AND GFS ARE IN REASONABLE AGREEMENT REGARDING THE
EVOLUTION OF WRN U.S. TROUGH INTO THE DAY3 PERIOD. A SUBSTANTIAL
MID-LEVEL JET STREAK SHOULD TRANSLATE THROUGH THE BASE OF THE TROUGH
BEFORE EJECTING ACROSS THE EDWARDS PLATEAU LATE IN THE PERIOD. THIS
SCENARIO FAVORS A LEE CYCLONE ACROSS THE SRN PLAINS WITH A SHARP DRY
LINE…LIKELY ARCING ACROSS NWRN-SWRN TX AT PEAK HEATING. WHILE
THERE IS SOME CONCERN THAT A COASTAL BOUNDARY MAY RETARD NWD
ADVANCEMENT OF BOUNDARY LAYER MOISTURE INTO NCNTRL TX…INCREASING
DIFLUENT HIGH-LEVEL FLOW AND APPROACHING SPEED MAX SUGGEST
MOISTENING WILL RAPIDLY SURGE NWD LATE IN THE PERIOD. IF THIS
MOISTURE RETURNS BY LATE AFTERNOON THEN SCT SUPERCELLS SHOULD
DEVELOP ALONG THE DRY LINE. STRENGTHENING SHEAR AND LARGE SCALE
ASCENT FAVOR NWD DEVELOPMENT INTO OK AFTER DARK.
…GULF STATES…
SEASONALLY STRONG MID-LEVEL FLOW IS EXPECTED TO CONTINUE ACROSS THE
SRN STATES THROUGH SUNDAY. ISOLATED THUNDERSTORMS MAY DEVELOP ALONG
SFC FRONT AS IT SAGS SWD TO NEAR I-20 BY 27/00Z…AND ALONG
FAVORABLE SEA-BREEZE CONVERGENT ZONES. IF CONFIDENCE INCREASES SUCH
THAT A MORE CONCENTRATED AREA OF CONVECTION WILL DEVELOP THEN SEVERE
PROBABILITIES MAY NEED TO BE INCREASED. FOR NOW WILL INTRODUCE 5
PERCENT SEVERE TO ACCOUNT FOR ISOLATED NATURE.
Precipitation Outlook
Two different storm systems and two different areas of precipitation are present in the 3 day precipitation outlook below. The eastern half of the country will be dealing with heavy rain and strong to severe thunderstorms through the first half of the weekend, while a western storm system will spread some much needed precipitation across the region through the entire weekend. Some of the heaviest moisture will be found from eastern Texas into the Gulf Coast states where thunderstorms develop, while some of the high elevations in the Western U.S. could see up to 1″+ possible!
Western Snowfall Potential
The snowfall potential through PM Sunday suggests up to 6″+ across parts of the mountains. Some of the heaviest looks to be across parts of the Sierra Nevada Range, Wasatch Range and across parts of the Rockies.
Warming into May
For folks in the eastern two-thirds of the nation, temperatures over the last week have been a little cooler than average. It has felt a little more like March rather than April. The good news is that extended forecasts are suggesting a nice warming trend as we head into next week. During the last few days of April/early May, most of us could get back to average if not even a little bit above. The image below shows NOAA’s temperature outlook from May 1st to May 7th.
Thanks for checking in and have a great weekend ahead! Don’t forget to follow me on Twitter @TNelsonWX
