011
FXUS61 KILN 261127
AFDILN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
627 AM EST TUE JAN 26 2021
SYNOPSIS
LOW PRESSURE WILL MOVE NORTHEAST THROUGH THE OHIO VALLEY TODAY,
WITH RAIN AND FOG EXPECTED THIS MORNING, AND SOME CHANCES FOR
RAIN CONTINUING INTO THE DAY. ANOTHER LOW PRESSURE SYSTEM WILL
PASS SOUTH OF THE AREA WEDNESDAY AFTERNOON AND EVENING, BRINGING
SOME SNOW TO THE REGION. HIGH PRESSURE WILL BRING DRIER
CONDITIONS ON THURSDAY AND FRIDAY.
NEAR TERM /UNTIL 6 PM THIS EVENING/
QUICK UPDATE TO MAKE A FEW ADJUSTMENTS TO PRECIPITATION CHANCES
(PRIMARILY TO FOCUS ON DRIZZLE) AND FOG.
IN ADDITION, THE WINTER WEATHER ADVISORY HAS EXPIRED AS PLANNED
AT 6 AM.
TO UPDATE THE SITUATION WITH THE FOG, WIDESPREAD VISIBILITIES OF
1/2SM TO 1 1/2SM HAVE OVERSPREAD MUCH OF THE ILN FORECAST AREA.
SO FAR, HOWEVER, VISIBILITIES HAVE NOT DROPPED TO 1/4SM, WHICH
IS PRECLUDING THE NEED FOR A DENSE FOG ADVISORY AS OF THIS
WRITING. HRRR VISIBILITY FORECASTS CONTINUE TO SUGGEST THAT THIS
FOG MAY CONTINUE TO WORSEN OVER THE NEXT FEW HOURS, AS THE WIDE
SWATH OF LOWEST VISIBILITIES GRADUALLY SHIFTS NORTHWARD.
HOWEVER, IT MAY BE A SCENARIO IN WHICH THE WORST OF THE ISSUE IS
SIMPLY THE PRESENCE OF THE VERY LOW STRATUS DECK, WHILE SURFACE
VISIBILITIES REMAIN JUST ABOVE DENSE FOG CRITERIA. IT IS ALSO
WORTH NOTING WHAT HAS OCCURRED UPSTREAM IN THE NWS LMK FORECAST
AREA -- ONCE THE WSW WINDS REALLY KICKED IN, VISIBILITIES
IMPROVED QUICKLY. SO, FOR NOW, THE SPECIAL WEATHER STATEMENT
APPROACH WILL BE MAINTAINED FOR THE ILN CWA.
PREVIOUS DISCUSSION (402 AM) >
ALTHOUGH HEAVIER PRECIPITATION HAS ENDED ACROSS THE ILN
FORECAST AREA, THIS FORECAST REMAINS SOMEWHAT COMPLICATED, WITH
SEVERAL ELEMENTS TO DISCUSS.
ONE ELEMENT TO THE FORECAST THAT SEEMS TO BE A DIMINISHING
THREAT IS THE POTENTIAL FOR HAZARDOUS WINTRY PRECIPITATION. A
WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR EIGHT ILN COUNTIES
IN THE NORTHERN PART OF THE FORECAST AREA, WHERE AIR
TEMPERATURES REMAIN RIGHT AROUND FREEZING, AND ROAD SURFACE
TEMPERATURES ARE PERHAPS A DEGREE OR TWO ABOVE FREEZING.
ALTHOUGH TEMPERATURES HAVE BEEN STUBBORNLY STEADY FOR THE PAST
FEW HOURS, A SLOW WARMING TREND SHOULD BEGIN SOON. AS IT IS, ICE
ACCUMULATIONS WILL LIKELY BE LIMITED TO ELEVATED SURFACES -- AND
PRECIPITATION HAS BECOME QUITE LIGHT ACROSS THE AREA. IT SEEMS
THE RIGHT IDEA TO KEEP THE ADVISORY IN EFFECT FOR A LITTLE
LONGER, BUT UNLESS THERE ARE SIGNS OF THINGS GOING AWRY, IT WILL
LIKELY MEET ITS PLANNED EXPIRATION AT 6 AM.
FOG, HOWEVER, IS EXPECTED TO BECOME A BIGGER ISSUE OVER THE NEXT
FEW HOURS. CURRENT OBSERVATIONS SHOW WIDESPREAD VISIBILITIES
BELOW 1SM (WITH SOME 1/4SM OBS) IN SOUTHEAST ILLINOIS, SOUTHERN
INDIANA, AND AREAS OF KENTUCKY NEAR AND WEST OF LOUISVILLE. THIS
THICK LOW-LEVEL MOISTURE IS GRADUALLY ADVECTING TO THE
NORTHEAST, AND WILL OVERSPREAD THE ILN CWA BETWEEN 5AM AND 8AM.
THE SIGNAL FOR THIS FOG ON THE HRRR HAS BEEN QUITE CONSISTENT
ALL NIGHT, WITH AN EXPECTATION THAT DENSE FOG WILL BE A
POSSIBILITY. ALTHOUGH FOG IS NOT ALWAYS EASY TO FORECAST (OR
ISSUE PRODUCTS FOR) IN ADVANCE, THE OBS/MODELS/METEOROLOGY
PROVIDE A REASONABLE AMOUNT OF CONFIDENCE THAT THIS WILL BECOME
AN ISSUE IN THE ILN CWA WITHIN A FEW HOURS, AFFECTING THE
MORNING COMMUTE. A SPECIAL WEATHER STATEMENT WAS ISSUED FOR THE
AREA OF THE CWA WHERE CONFIDENCE IS HIGHEST, AND IT WOULD NOT BE
SURPRISING IF THIS STATEMENT NEEDS TO BE RE-ISSUED AND EXPANDED,
OR EVEN IF A DENSE FOG ADVISORY MAY BECOME NECESSARY.
THE PRECIPITATION FORECAST TODAY IS LARGELY BASED ON LOW-END
DRIZZLE AND SHOWER POTENTIAL, WITHOUT MUCH IN THE WAY OF FORCING
OR DEEP-LAYER MOISTURE. THE FRONTAL STRUCTURE OVER THE AREA
RIGHT NOW IS SOMEWHAT CONVOLUTED. THERE IS A BROAD/WEAK SURFACE
LOW SOMEWHERE IN THE CINCINNATI AREA RIGHT NOW, AND THIS LOW
WILL BE MOVING NORTHEAST FROM HERE THROUGH THE MORNING. A MORE
SIGNIFICANT POOL OF HIGHER THETA-E AIR WILL BE LARGELY MISSING
THE ILN CWA TO THE SOUTHEAST, BUT FLOW ON THE BACK SIDE OF A
FRONTAL BOUNDARY WILL SWITCH WINDS TO THE SOUTHWEST -- AMONG
OTHER THINGS, HELPING TO ADVECT THE FOG INTO THE AREA THIS
MORNING, AND THEN ALSO HELPING TO VERY SLIGHTLY MIX OUT SOME OF
THE SURFACE MOISTURE LATER IN THE DAY. THERE IS ALSO EXPECTED
TO BE AN OCCLUDED BOUNDARY EXTENDING WSW FROM THE LOW CENTER,
AND THIS BOUNDARY WILL SET UP ACROSS THE NORTHERN SECTIONS OF
THE FORECAST AREA LATER THIS MORNING. ALL IN ALL, THERE WILL BE
COPIOUS LOW-LEVEL MOISTURE, BUT WEAK FORCING IN THE VICINITY OF
THE FRONT, AND SOME GENTLE ASCENT IN THE SOUTHWESTERLY FLOW TO
THE SOUTH OF THE FRONT. IT IS A SETUP THAT LOOKS MORE FAVORABLE
FOR PATCHY DRIZZLE THAN ANYTHING ELSE, PERHAPS WITH A FEW
LEGITIMATE SHOWERS DEVELOPING IN THE NORTHERN SECTIONS OF THE
FORECAST AREA. THE GOOD NEWS IS THAT ALL SIGNS POINT TO THIS
PRECIPITATION FALLING AS RAIN, MAYBE MIXING WITH SOME SNOW (WITH
NO ACCUMULATIONS) LATE IN THE DAY NORTH OF INTERSTATE 70. WITH
THE FRONT IN THE AREA, THE TEMPERATURE GRADIENT SHOULD BE FAIRLY
STRONG -- WITH HIGHS RANGING FROM THE MID 30S (NW) TO LOWER 50S
(SE). IN THE SOUTHERN AND SOUTHEASTERN SECTIONS OF THE FORECAST
AREA, SOME WIND GUSTS TO AROUND 25 MPH WILL BE POSSIBLE THIS
AFTERNOON.
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/
THERE MAY STILL BE SOME LIGHT PRECIPITATION IN THE CENTRAL OHIO
AREA THIS EVENING, BUT DRY CONDITIONS ARE EXPECTED THEREAFTER,
AS THE FRONT BEGINS TO MOVE SOUTHWEST AS A COLD FRONT -- AND
DRIER AIR ADVECTS INTO THE AREA. THIS MAY NOT BE ENOUGH TO CLEAR
UP THE THICK LOW CLOUDS, BUT IT SHOULD BRING AN END TO
PRECIPITATION CHANCES.
ATTENTION WILL THEN FOCUS ON A SHORTWAVE MOVING INTO THE AREA
LATE ON WEDNESDAY. AFTER A BRIEF PERIOD OF HEIGHT RISES ON
WEDNESDAY MORNING, THIS WAVE WILL MOVE EAST ACROSS MISSOURI AND
KENTUCKY, SPREADING SOME PRECIPITATION INTO THE ILN FORECAST
AREA AFTER 18Z. THIS SYSTEM WILL BE COVERED IN DETAIL IN THE
LONG TERM SECTION, BUT IT IS WORTH NOTING HERE THAT SOME
ACCUMULATING SNOW MAY ALREADY BE ONGOING IN THE SOUTHWESTERN ILN
CWA BEFORE 00Z.
LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/
A MID LEVEL SHORTWAVE TO TRACK FROM THE CENTRAL PLAINS THRU THE
OHIO VALLEY WED/WED NIGHT. ASSOCIATED SURFACE LOW PRESSURE TO
TRACK THRU THE TENNESSEE VALLEY. THIS PLACES ILN/S SOUTHERN
COUNTIES ON THE NORTHERN PERIPHERY OF THE PRECIPITATION SHIELD.
ALTHOUGH EXPECTED SOLUTION DIFFERENCES EXIST AT THIS TIME --
MODEL SOLUTIONS ARE GENERALLY IN BETTER AGREEMENT. BOTH THE
ECMWF AND GFS ENSEMBLE PROBABILITIES FOR AN INCH OF SNOW WED/WED
NIGHT ALONG AND SOUTH OF THE OHIO RIVER IS AT 60 TO 70+
PERCENT. GFS IS POSITIONED SLIGHTLY FURTHER SOUTH WITH THE NAM
BEING THE FURTHEST SOUTH. STORM TOTAL SNOW OF 1 TO 2 INCHES
LOOKS POSSIBLE FROM THIS EVENT THROUGH WEDNESDAY EVENING WITH
SOME UNCERTAINTY EXISTING REGARDING EXACT PLACEMENT.
THE SHORTWAVE AND LOW ARE PROGRESSIVE AND QUICKLY MOVE OFF TO
THE EAST THURSDAY. NORTHWEST FLOW REGIME DEVELOPS WITH SURFACE
HIGH PRESSURE BUILDING IN FOR THURSDAY AND FRIDAY OFFERING DRY
WEATHER AND COLDER TEMPERATURES.
TEMPERATURES LOOK TO BE A LITTLE BELOW NORMAL THURSDAY WITH
HIGHS FROM THE MID 20S NORTH TO THE LOWER 30S SOUTH. READINGS A
LITTLE CLOSER TO NORMAL FRIDAY WITH HIGHS RANGING FROM THE UPPER
20S NORTH TO THE UPPER 30S SOUTH.
FLOW BACKS WITH AN INCREASE IN MOISTURE AS NEXT SHORTWAVE AND
SFC LOW TRACK FROM THE CENTRAL PLAINS INTO THE GREAT LAKES THIS
WEEKEND. THIS IS A COMPLEX SYSTEM AND MODEL SOLUTION TIMING
DIFFERENCES EXIST REGARDING THE ONSET AND PROGRESSION OF THE
PRECIPITATION. WILL RAMP UP POPS SATURDAY NIGHT INTO SUNDAY WITH
CATEGORICAL TO LIKELY POPS ACROSS THE AREA. A SIGNAL EXISTS
POINTING FOR THE POTENTIAL FOR ACCUMULATING SNOW SATURDAY
NIGHT/EARLY SUNDAY AS LOW LEVEL JET/ISENTROPIC LIFT COME INTO
PLAY AND THERMAL PROFILES ARE COLD ENOUGH FOR SNOW -- ESPECIALLY
ACROSS THE NORTHWEST/NORTH COUNTIES. TOO EARLY TO PINPOINT
AMOUNTS OR PLACEMENT BUT WILL HAVE TO SEE HOW THIS SYSTEM
EVOLVES. EVENTUALLY, UNDER THE INFLUENCE OF WAA PCPN CHANGES
OVER TO RAIN IN MOST LOCATIONS SUNDAY. WITH THE UPPER TROF
COMING ACROSS THE AREA CHANCE POPS CONTINUE MONDAY WITH A
TRANSITION BACK TO LIGHT SNOW.
TEMPERATURE WISE...HIGHS TO RANGE FROM THE LOWER 30S NORTHEAST
TO LOWER 40S SOUTHWEST ON SATURDAY, AND THEN UPPER 30S TO NEAR
50 SUNDAY, DROPPING BACK TO LOWER 30S TO UPPER 30S MONDAY.
AVIATION /12Z TUESDAY THROUGH SATURDAY/
PATCHY DRIZZLE WILL CONTINUE TO IMPACT THE TAF SITES THROUGH
THE MORNING HOURS. HOWEVER, IT APPEARS THAT FREEZING
PRECIPITATION HAS ENDED AT THE AIRPORTS, SO ONLY -DZ IS
EXPECTED FROM THIS POINT FORWARD.
THE MAIN ISSUE WILL BE VERY LOW CEILINGS AND VISIBILITIES. THE
POOR VISIBILITIES ARE EXPECTED TO CONTINUE FOR ANOTHER FEW
HOURS, AND THE POOR CEILINGS WILL CONTINUE WELL INTO THE DAY
TODAY. RIGHT NOW, CEILINGS ARE LIFR AT ALL TAF SITES.
VISIBILITIES ARE GENERALLY IN THE 1/2SM TO 1 1/2SM RANGE, THOUGH
SOME TOWER VISIBILITIES HAVE BEEN 1/4SM AT TIMES. THE TAFS ARE
TIMED OUT TO SHOW A NORTHWARD PROGRESSION OF THE SLOW
IMPROVEMENT -- FIRST TO VISIBILITIES, AND THEN TO CEILINGS.
HOWEVER, CEILINGS WILL REMAIN NO BETTER THAN THE LOW END OF THE
MVFR CATEGORY THIS AFTERNOON.
SOME DRIZZLE OR LIGHT RAIN WILL BE POSSIBLE LATER TODAY,
PARTICULARLY AT KCMH/KLCK, BUT WITH NO IMPACTS EXPECTED. WINDS
WILL ALSO INCREASE SLIGHTLY OUT OF THE SOUTHWEST, WITH SOME
GUSTS TO AROUND 20KTS POSSIBLE.
OVERNIGHT TONIGHT, CEILINGS MAY LOWER TO THE IFR CATEGORY AGAIN,
AS WINDS TURN FROM THE WEST TO THE NORTH AND EVENTUALLY TO THE
NORTHEAST.
OUTLOOK... MVFR/IFR CONDITIONS WILL PERSIST THROUGH WEDNESDAY
NIGHT. SOME SNOW IS POSSIBLE ON WEDNESDAY NIGHT, PARTICULARLY
FOR KCVG/KLUK.
ILN WATCHES/WARNINGS/ADVISORIES
OH...NONE.
KY...NONE.
IN...NONE.
SYNOPSIS...HATZOS
NEAR TERM...HATZOS
SHORT TERM...HATZOS
LONG TERM...AR
AVIATION...HATZOS
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