128
FXUS63 KILX 160355 CCA
AFDILX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE LINCOLN IL
859 PM CST FRI NOV 15 2024
KEY MESSAGES
- AREAS OF FOG ARE LIKELY (60-80% CHANCE) LATE TONIGHT FROM I-55
WESTWARD WHERE VISIBILITY MAY FALL BELOW ONE-HALF MILE.
- RAIN RETURNS MONDAY, WITH A SLIGHT (20%) CHANCE FOR EMBEDDED
THUNDERSTORMS BY MONDAY EVENING IN AREAS SOUTH OF INTERSTATE 72.
RAIN WILL BE ACCOMPANIED BY GUSTY WINDS, PARTICULARLY MONDAY
EVENING WITH AVERAGE GUSTS BETWEEN 30-40 MPH.
- TEMPERATURES WILL TURN SHARPLY COLDER BY THE MIDDLE OF NEXT
WEEK, BUT HOW COLD AND FOR HOW LONG REMAINS HIGHLY UNCERTAIN,
ALONG WITH ANY PROSPECTS FOR ACCUMULATING SNOW.
UPDATE
ISSUED AT 859 PM CST FRI NOV 15 2024
FOG POTENTIAL CONTINUES TO BE THE MAIN FORECAST QUESTION FOR
TONIGHT. ALTHOUGH HIGH PRESSURE CONTINUES TO SLIP EASTWARD,
CAUSING A LIGHT SOUTHEAST FLOW TO BEGIN ACROSS THE AREA, SOME
LOWERING OF VISIBILITY HAS BEEN DEVELOPING OUTSIDE OF A LOW CLOUD
DECK THAT REMAINS ENTRENCHED OVER EASTERN IL. THIS CLOUD DECK
SHOULD HELP PREVENT ANY SIGNIFICANT FOG, BUT HOW FAR WESTWARD IT
SPREADS REMAINS IN QUESTION. IN ADDITION, A SUBTLE INCREASE IN
WINDS OVERNIGHT SHOULD HELP MITIGATE FOG DEVELOPMENT. WILL ADD
AREAS ALONG THE I-55 CORRIDOR AND WESTWARD TO PATCHY FOG MENTION
OVERNIGHT GIVEN THE SLOWER ADVANCE OF LOW CLOUD COVER WESTWARD
VERSUS THE AFTERNOON FORECAST PACKAGE. OTHERWISE, LOWS FROM THE
UPPER 30S TO LOWER 40S CONTINUE TO LOOK GOOD FOR TONIGHT.
37
DISCUSSION
ISSUED AT 1227 PM CST FRI NOV 15 2024
THE MAIN FORECAST CHALLENGE IN THE NEAR TERM IS PINNING THE FOG
POTENTIAL LATE TONIGHT INTO SATURDAY MORNING.
SHORT-TERM GUIDANCE REMAINS INCONSISTENT WITH VISIBILITY
OVERNIGHT, WITH THE HRRR, NAMNEST, RAP, AND ARW ALL SHOWING
POCKETS OF SUB- HALF-MILE VISIBILITY, PRIMARILY WEST OF A PEORIA
TO SPRINGFIELD LINE. WORTH MENTIONING, THOUGH, IS THE DETERMINISTIC
HRRR WHICH SUPPORTS TRANSIENT SUB- HALF- MILE VISIBILITY AS FAR
EAST OF I-57 OVERNIGHT. GLANCING AT THE MOST RECENT PROBABILISTIC
HREF GUIDANCE, THERE IS A 60-80% CHANCE FOR SUB- HALF- MILE
VISIBILITY ACROSS WEST CENTRAL ILLINOIS TONIGHT. THIS, ALONGSIDE
A FAVORABLE SYNOPTIC SETUP IN WHICH (A) SKIES WILL BE CLEAR, (B)
WINDS WILL BE CALM, AND (C) SHALLOW MOISTURE WILL BECOME TRAPPED
BENEATH A SUBSIDENCE INVERSION, HAS PROMPTED US TO ADD FOG TO OUR
GRIDDED FORECAST IN AREAS WEST OF A PEORIA-TO-SPRINGFIELD LINE FOR
LATE TONIGHT. TRENDS WILL BE MONITORED THIS EVENING ON WHETHER A
DENSE FOG ADVISORY MAY BE NEEDED, BUT THE ANSWER IS CURRENTLY
UNCLEAR WITH A GOOD CHUNK OF ILLINOIS LIKELY BECOMING SHROUDED IN
LOW STRATUS.
ATTENTION THEN TURNS TO MONDAY AS A ROBUST UPPER TROUGH LIFTS
FROM BAJA CALIFORNIA AND PIVOTS ACROSS THE CENTRAL PLAINS, WITH
ITS ATTENDANT SURFACE LOW OCCLUDING OVER THE UPPER MIDWEST. THE
MOISTURE FLUX AHEAD OF THIS WAVE LOOKS RATHER ROBUST AS PWATS
APPROACH THE 95TH PERCENTILE FOR MID- NOVEMBER CLIMATOLOGY.
RAINFALL ASSOCIATED WITH THIS WAVE LOOKS TO COME IN TWO WAVES: (1)
EARLY MONDAY MORNING ALONG THE WARM FRONT, WITHIN A WARM-
ADVECTION REGIME, AND THEN (2) MONDAY EVENING AHEAD OF THE COLD
FRONT. MODEL QPF FROM BOTH BLENDED (NBM) AND ENSEMBLE (LREF)
GUIDANCE SUGGESTS OUR RAINFALL GOALPOSTS (10TH-90TH) WILL RANGE
BETWEEN 0.25" - 1" IN AREAS NORTH OF I-70. WHILE SEVERE WEATHER
IS NOT CURRENTLY ANTICIPATED, BLENDED GUIDANCE POINTS TO A SLIGHT
CHANCE (20%) OF THUNDER MONDAY EVENING AS A STRONG LLJ NOSES INTO
THE REGION AND PROVIDES A FEW HUNDRED J/KG OF MUCAPE, WHICH COULD
BE ENOUGH TO SUPPORT AN ATTENDANT WIND RISK. BUT EVEN IF IT DOES
NOT STORM, SYNOPTIC WINDS WILL BE GUSTY, WITH THE ENSEMBLE MEAN
FROM BOTH THE GEFS & EPS GENERALLY IN THE 30-40 MPH RANGE.
AS WE HEAD INTO THE MIDDLE OF NEXT WEEK, THERE REMAINS LARGE
VARIANCE AMONG GLOBAL ENSEMBLE SYSTEMS (GEFS, EPS AND GEPS) WITH
RESPECT TO HOW THE OCCLUDED SURFACE LOW PHASES TOGETHER WITH ANOTHER
DIGGING TROUGH COMING OUT OF THE PACIFIC NORTHWEST. THE MAJORITY
OF THE GUIDANCE SUPPORTS A HIGHLY AMPLIFIED PATTERN WITH GUSTY
WINDS AND MUCH COLDER TEMPERATURES SPILLING ACROSS THE MIDWEST.
THE POSITION AND AMPLITUDE OF THIS UPPER LOW WILL DETERMINE HOW
WINDY AND HOW COLD WE WILL GET, AS WELL AS HOW LONG THE COLD WILL
STICK AROUND. WHILE THAT IS INTENTIONALLY VAGUE, WE CAN LOOK
TOWARD THE ENSEMBLE MEAN FOR A REASONABLE FIRST GUESS FOR MID-WEEK
GUSTS, WHICH CURRENTLY SUPPORT 30-40 MPH. MEANWHILE, TEMPERATURE
SPREADS FOR LATE NEXT WEEK ARE LARGE, BUT WE COULD RETURN TO SUB-
FREEZING OVERNIGHT LOWS AS EARLY AS WEDNESDAY NIGHT. AND, WITH
SHOWERY PRECIP LIKELY WITHIN A STRONG COLD ADVECTION REGIME, IT
REMAINS A GOOD POSSIBILITY THAT WE SQUEEZE OUT THE SEASON'S FIRST
SNOWFLAKES ACROSS OUR NORTHERN HALF.
MJA
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 551 PM CST FRI NOV 15 2024
AS HIGH PRESSURE SHIFTS EASTWARD TONIGHT, SOUTHEASTERLY FLOW WILL
START TO PUSH LOW CLOUD COVER CURRENTLY LINGERING IN EASTERN IL
WESTWARD INTO THE CENTRAL IL TERMINALS, ESPECIALLY THOSE FROM
KDEC-KBMI EASTWARD. TO THE WEST, FOG COULD DEVELOP IF CLOUD COVER
DOESN'T SPREAD THAT FAR WESTWARD, CREATING SOME UNCERTAINTY ABOUT
THE CHARACTER OF AVIATION CONCERNS BETWEEN LOW CEILINGS AND/OR
FOG. FOR NOW, HAVE INCLUDED MVFR CIGS FROM KBMI-KDEC EASTWARD
STARTING 06Z-09Z, AND FOR KPIA AND KSPI DETERIORATED CONDITIONS TO
IFR FROM AROUND 10Z-15Z, WITH FOG AND LOW CIGS MENTIONED IN TAF.
CONDITIONS SHOULD IMPROVE TO VFR AROUND 16Z AS SOUTHERLY FLOW
CONTINUES TO INCREASE. WINDS SE UNDER 5 KTS INITIALLY, INCREASING
TO 10-12 KTS AND BECOMING SSE BY 16Z.
37
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
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