360
FXUS63 KLSX 240833
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
233 AM CST FRI JAN 24 2025
KEY MESSAGES
- WE BEGIN TO EMERGE FROM OUR COLD SPELL TODAY AND SATURDAY WITH
MORE MILD TEMPERATURES EXPECTED FOR MOST OF THIS WEEKEND AND
NEXT WEEK.
- DRY WEATHER LASTS THROUGH AT LEAST THE FIRST HALF OF NEXT WEEK,
WITH PRECIPITATION CHANCES INCREASING FOR THE MIDDLE TO LATER
PART OF THE WEEK.
SHORT TERM
(THROUGH LATE SATURDAY AFTERNOON)
ISSUED AT 231 AM CST FRI JAN 24 2025
OUR PERSISTENT COLD WEATHER PATTERN IS FINALLY BEGINNING TO CHANGE.
THE LAST OF THE COLD CORE UPPER TROUGH IS MOVING EAST AND OUT OF OUR
AREA TODAY. BEHIND IT WE'LL SEE RISING MID LEVEL HEIGHTS AND WARMING
TEMPERATURES ALOFT. SURFACE HIGH PRESSURE OVER THE SOUTHERN PLAINS
ALSO SHIFTS EASTWARD TOWARD THE LOWER MISSISSIPPI VALLEY TODAY,
OPENING US UP TO A SOUTHWESTERLY LOW LEVEL FLOW. SO DESPITE A VERY
COLD START, WE'LL SEE A STRONG REBOUND IN TEMPERATURES TODAY,
ESPECIALLY ACROSS MUCH OF MISSOURI WHERE WARM ADVECTION WILL BE
STRONGEST. VERY DRY AIR IN PLACE WILL ENABLE A STRONG WARM UP AS
INCOMING SOLAR ENERGY MORE EFFICIENTLY WARMS A DRY AIR MASS.
SOUTHWEST LOW LEVEL FLOW WILL PROMOTE DOWNSLOPING OFF THE OZARKS
ESPECIALLY ACROSS CENTRAL AND EASTERN MISSOURI, FURTHER AIDING IN
MIXING OF THOSE WARMER TEMPERATURES FROM ALOFT DOWN TOWARD THE
SURFACE. THESE FIRST DAYS EMERGING FROM A COLD AIR MASS TYPICALLY
WARM MORE STRONGLY THAN GUIDANCE WOULD SUGGEST, AND WE HAVE
INCREASED FORECAST TEMPERATURES TODAY BY ABOUT 5 DEGREES OVER THE
NBM AND PRIOR FORECAST VALUES. WITH FULL MIXING THIS MAY NOT BE WARM
ENOUGH, AS PROJECTED 850MB TEMPERATURES AROUND MIDDAY SUGGEST LOW TO
MID 40S ARE POSSIBLE. FURTHER EAST ACROSS ILLINOIS THE COLD AIR MASS
WILL BE SLOWER TO LEAVE, SO WE HAVE STUCK CLOSER TO NBM GUIDANCE
WHICH HOLDS TEMPERATURES NEAR OR BELOW FREEZING FOR ONE MORE DAY.
THE HIGH CONTINUES TO MOVE EAST TONIGHT INTO SATURDAY, WITH
SOUTHWEST FLOW PERSISTING AHEAD OF THE NEXT COLD FRONT BEING DRIVEN
BY A TROUGH MOVING EAST THROUGH THE GREAT LAKES. WITH WINDS LIKELY
TO REMAIN SOMEWHAT ELEVATED THROUGH THE NIGHT, TEMPERATURES WON'T
COOL AS WELL TONIGHT. WE'VE LEANED THE FORECAST MORE TOWARD THE NBM
90TH PERCENTILE (THE WARM SIDE) IN THIS TIME PERIOD TO ACCOUNT FOR
THAT CONTINUED LOW LEVEL MIXING. THE COLD FRONT WILL BE ENTERING THE
NORTHERN PART OF THE FORECAST AREA DURING THE DAY ON SATURDAY, WITH
THE COLDER AIR BEHIND THE FRONT STALLING FURTHER WARMING. BUT AHEAD
OF THE FRONT WE'LL SEE A MILD DAY WITH SOUTHWEST TO WESTERLY FLOW
MAINTAINING A WELL MIXED LOW LEVEL ENVIRONMENT AND TEMPERATURES IN
THE 40S TO LOW 50S. INCREASED CLOUD COVER AHEAD OF THE FRONT COULD
REDUCE THE HIGH END POTENTIAL FOR TEMPERATURES AS WE WON'T HAVE AS
STRONG OF SUNSHINE TO WORK WITH. HOWEVER, THE PRESSURE GRADIENT
AHEAD OF THE FRONT IS LIKELY ENOUGH TO ENSURE GOOD MIXING AHEAD OF
THE FRONT WITH TEMPERATURES REACHING THE UPPER 40S TO LOW 50S. IF
CLOUDS ARE LESS EXTENSIVE, WE COULD WARM MORE SOLIDLY INTO THE 50S
BEFORE THAT FRONT ARRIVES.
KIMBLE
LONG TERM
(SATURDAY NIGHT THROUGH THURSDAY)
ISSUED AT 231 AM CST FRI JAN 24 2025
THE UPPER LEVEL FLOW PATTERN ACROSS NORTH AMERICA IS BEGINNING TO
CHANGE. WHILE THE COLD TROUGH OVER THE CENTRAL US MOVES EAST,
ANOTHER TROUGH DIGS SOUTH ALONG THE WEST COAST THIS WEEKEND,
BECOMING CUT OFF OVER CALIFORNIA. TO THE NORTH OF THIS, RIDGING
BECOMES ESTABLISHED OVER BRITISH COLUMBIA. THIS HIGH AMPLITUDE RIDGE
SETS UP NORTHWEST FLOW IN THE NORTHERN STREAM CONTINUING THE FLOW OF
CONTINENTAL AIR INTO THE CENTRAL US. WHILE NORTHWEST FLOW OFTEN
SENDS COLD AIR MASSES SOUTHWARD, THE AIR CIRCULATING AROUND THE
RIDGE IS MORE OF A MODIFIED NORTH PACIFIC AIR MASS, SO AFTER A BRIEF
COOL DOWN BEHIND SATURDAY'S FRONT, WE'LL ACTUALLY SEE SOME MILD AIR
FOR A WHILE. SURFACE HIGH PRESSURE PUSHES SOUTHWARD THROUGH THE AREA
ON SUNDAY WITH TEMPERATURES SOME 10 TO 15 DEGREES COOLER THAN
SATURDAY. BUT ONCE THAT HIGH MOVES SOUTH A WESTERLY LOW LEVEL FLOW
BEGINS ACROSS THE CENTRAL PLAINS AND MILD AIR QUICKLY RETURNS. HIGH
PRESSURE PUSHING SOUTHWARD ALSO HAS THE EFFECT OF BLOCKING GULF
MOISTURE, SO WE'LL STAY LARGELY DRY FOR A WHILE.
THE CUT OFF LOW WILL WOBBLE OVER THE SOUTHWEST US FOR SEVERAL DAYS.
CURRENT GUIDANCE SUGGESTS AN INITIAL SHORTWAVE EJECTS OUT OF THAT
LOW AND EASTWARD ACROSS THE SOUTHERN TIER OF THE COUNTRY TUESDAY
INTO WEDNESDAY. THIS SHOULD STAY LARGELY SOUTH OF OUR AREA, AND WITH
MOISTURE RETURN BEING BLOCKED PRECIPITATION CHANCES WITH THIS REMAIN
LOW. A NORTHERN STREAM TROUGH ALSO DIGS INTO THE GREAT LAKES AROUND
THE SAME TIME FRAME, THIS TIME ACCOMPANIED BY A MUCH COLDER ARCTIC
AIR MASS BEHIND IT. GUIDANCE IS STILL VARIABLE ON WHERE THIS COLD
AIR MASS HEADS. A MAJORITY OF THE GUIDANCE SENDS THE CORE OF THIS
COLD FURTHER EAST TOWARD NEW ENGLAND WITH US GETTING MORE OF A
GLANCING BLOW, BUT SOME GUIDANCE SENDS A SIGNIFICANT PORTION
SOUTHWARD TOWARD OUR AREA. THIS RESULTS IN GREATER UNCERTAINTY IN
THE TEMPERATURE FORECAST IN THE MIDDLE TO LATER PART OF THE WEEK.
THIS UNCERTAINTY IS SHOWN IN PART BY THE NBM INTERQUARTILE RANGE FOR
HIGH TEMPERATURES RISING TO 10 DEGREES OR HIGHER FROM WEDNESDAY
ONWARD. WHILE THE FORECAST AT THIS POINT REPRESENTS SOMEWHAT OF A
MIDDLE GROUND, IT'S POSSIBLE THAT WE DROP BACK BELOW NORMAL LATER IN
THE WEEK, IN THE 30S FOR HIGHS, OR WE STAY MORE MILD IN THE MID 40S
TO LOW 50S.
THE CORE OF THE SOUTHWEST US UPPER LOW DOESN'T MOVE OUT INTO THE
PLAINS UNTIL LATE IN THE WEEK, BUT WHEN IT DOES SO IT WILL SERVE AS
OUR NEXT BEST CHANCE FOR PRECIPITATION. AS IS TYPICAL WITH EJECTING
CUT OFF LOWS, THERE'S CONSIDERABLE UNCERTAINTY ON THE TIMING OF WHEN
THIS OCCURS. SOME GUIDANCE (AS REPRESENTED BY THE 00Z ECMWF) MOVE
THIS THROUGH OUR REGION THURSDAY INTO FRIDAY, WHILE OTHERS (AS
REPRESENTED BY THE 00Z GFS) DON'T BRING IT THROUGH UNTIL SATURDAY.
WHEN IT DOES MOVE THROUGH THERE WILL LIKELY BE A BETTER GULF
MOISTURE CONNECTION, SUPPORTING THE IDEA OF AT LEAST SOME
PRECIPITATION. WHAT TYPE WILL DEPEND ON HOW MUCH COLD AIR LINGERS IN
ADVANCE OF IT. GIVEN THE SETUP, ALL TYPES OF WINTRY PRECIPITATION
WILL BE POSSIBLE IF ENOUGH COLD AIR LINGERS IN THE LOW LEVELS. IF
THAT COLD AIR IS LESS INTENSE OR MORE EASILY SHOVED ASIDE, THEN
PRECIPITATION WILL BE MOSTLY RAIN. PRECIPITATION CHANCES AT THE TAIL
END OF THIS 7-DAY FORECAST REMAIN SOMEWHAT LOW PRIMARILY DUE TO THAT
RATHER LARGE TIMING UNCERTAINTY. IT'S LIKELY WE GET PRECIPITATION
OUT OF THIS, IT'S JUST A MATTER OF WHEN, AND IT COULD BE JUST
OUTSIDE OUR CURRENT 7-DAY FORECAST.
KIMBLE
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1035 PM CST THU JAN 23 2025
VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD. LIGHT AND
VARIABLE WINDS WILL INCREASE FROM THE SOUTHWEST LATE FRIDAY
MORNING AND REMAIN STEADILY AROUND 10 KTS THROUGH THE REST OF THE
PERIOD. LLWS MAY BE A CONCERN FRIDAY NIGHT, ESPECIALLY IN MID-
MISSOURI THROUGH WEST-CENTRAL ILLINOIS WHERE A NOCTURNAL ~45 KT LLJ
IS FORECAST TO STRENGTHEN. HOWEVER, CONFIDENCE IN IMPACTS IS TOO
LOW TO INCLUDE IN THE TAFS DURING THIS PACKAGE.
JAJA
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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