207
FXUS63 KAPX 181836
AFDAPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
236 PM EDT TUE AUG 18 2026
KEY MESSAGES
- SHOWERS LIKELY AND CHANCE OF THUNDERSTORMS THIS AFTERNOON/EVENING.
A FEW STRONG STORMS POSSIBLE.
- QUIET WEDNESDAY-THURSDAY
- UNSETTLED AGAIN THURSDAY NIGHT INTO THIS WEEKEND.
DISCUSSION
ISSUED AT 236 PM EDT TUE AUG 18 2026
PATTERN / FORECAST SYNOPSIS:
DISHEVELED LONGWAVE TROUGHING OVER NORTHEASTERN NORTH AMERICA TO BE
THE PRIMARY INFLUENCE OF THE REGION OVER THE FORECAST PERIOD, WITH
OCCASIONAL SHORTWAVE TROUGH PASSAGES TO MOVE THROUGH THE REGION,
MOST OF WHICH WILL BE MATURING / CLOSED OFF, AND MAY HAVE SOME
HANGTIME ACROSS THE GREAT LAKES OWING TO STANDARD STAGNANT AUGUST
JET DYNAMICS.
CURRENTLY, A MATURE UPPER LOW OVER HUDSON BAY TO CONTINUE AN
EASTWARD TREK, WITH ANTECEDENT SW RETURN FLOW DRAWING IN WARMER AND
(TO AN EXTENT) MORE MOIST AIR ACROSS THE GREAT LAKES. SURFACE
DEWPOINTS HAVE ALREADY BALLOONED TO THE 60 TO 66 RANGE ACROSS THE
REGION AS OF THE NOON HOUR, WITH EVIDENCE OF PREFRONTAL CLEARING
BUILDING INTO NORTHERN MICHIGAN. SURFACE COLD FRONTAL BOUNDARY
ROUGHLY STRETCHING FROM JAMES BAY THROUGH MARQUETTE AND WSW THROUGH
MINNESOTA JUST NORTH OF THE TWIN CITIES. EVIDENCE OF SOME MIXING
TRYING TO MANIFEST JUST AHEAD OF THIS COLD FRONTAL BOUNDARY... WHICH
MAY BE SOMETHING TO WATCH FOR ACROSS OUR NECK OF THE WOODS.
NONETHELESS, FRONTAL BOUNDARY TO PASS THROUGH THE REGION WITH JUST
ENOUGH INSTABILITY TO FORCE A CONVECTIVE RESPONSE ACROSS WISCONSIN,
EVENTUALLY LEAKING INTO NORTHERN LOWER LATE THIS AFTERNOON INTO THE
EVENING, WITH SHOWERS AND STORMS GRADUALLY CLEARING THROUGH THE
EVENING / NIGHT FROM WNW TO ESE.
SURFACE HIGH PRESSURE TO BUILD ON THE BACKSIDE OF THE FRONT,
YIELDING AN AGGRESSIVE DRYING NW WIND REGIME (IN CONJUNCTION WITH
500MB HEIGHT RISES / SHORTWAVE RIDGING) THROUGH THE DAY WEDNESDAY
THAT WILL BRING BACK SUNNIER SKIES AND SEASONABLE WARMTH DURING THE
DAY AND AGAIN THURSDAY... BUT WITH THE DRY NATURE OF THE AIRMASS AND
CALMING WINDS OVERNIGHT, COOLER NIGHTS TO RETURN WEDNESDAY AND
THURSDAY NIGHTS. NEXT WAVE DIGS FROM THE NNW STARTING FRIDAY, WITH
CURRENT TREND POINTING TO THIS WAVE OCCLUDING / CLOSING OFF OVERHEAD
THROUGH THE COURSE OF THE WEEKEND, BRINGING BACK COOLER AND
UNSETTLED CONDITIONS FOR AT LEAST THE START OF THE WEEKEND (AND
PERHAPS A RENEWED SEVERE THREAT FRIDAY?). HIGH PRESSURE / 500MB
SHORTWAVE RIDGING TO FOLLOW THROUGH THE DAY SUNDAY AND INTO MONDAY
BEFORE THE NEXT WAVE PASSES THROUGH AT THE END OF THE FORECAST
PERIOD.
DETAILS:
SHOWER / STORM POTENTIAL THIS AFTERNOON / TONIGHT: AFOREMENTIONED
FRONTAL BOUNDARY TO TRAVERSE THE REGION THIS EVENING INTO TONIGHT,
WHICH LOOKS TO SUFFICE IN THE FORCING DEPARTMENT (ALBEIT, TO A
LIMITED EXTENT... AS POINTED OUT BY PREVIOUS FORECASTER, FRONTAL
CONVERGENCE LEAVES A BIT TO BE DESIRED). LATEST CAMS SEEM BOUND AND
DETERMINED TO HAVE AN AGGRESSIVE PREFRONTAL MIXING REGIME,
PARTICULARLY ACROSS NORTHEAST LOWER WITH DOWNSLOPING WSW WINDS. WILL
HAVE TO SEE HOW AGGRESSIVE THIS TRENDS AS IT WILL BE PIVOTAL TO THE
GENERATION OF THIS EVENING'S INSTABILITY, AND THUS THE EVOLUTION OF
ANY CONVECTION. NONETHELESS, THE OTHER THING CAMS ARE PERSISTENT
WITH IS DEEPER MOISTURE RIGHT ALONG / AHEAD OF THE FRONT POOLING
ACROSS THE REGION, AND THUS GIVING US INSTABILITY IN THE ORDER OF
500 TO 800 J/KG OF MLCAPE. SEVERAL FASCINATING ASPECTS TO THIS SETUP
TO UNPACK... FIRST AND FOREMOST, MOST MODELED SOUNDINGS SHOWCASE A
PSEUDO-INVERTED-V PROFILE THAT USUALLY COMES WITH GUSTIER STORMS
THAT DON'T REALLY PRODUCE MUCH IN THE WAY OF RAINFALL... BUT WITH
LARGELY UNIDIRECTIONAL FLOW, ANTICIPATE IT IS POSSIBLE IF (AND IT'S
A BIG OLE "IF") WE CAN MAINTAIN INSTABILITY FOLLOWING ANY INTIAL
CONVECTION, WHICH COULD SUPPORT INCREASINGLY HEAVIER RAINFALL IN ANY
ADDITIONAL STORM FORMATION. A MAJORITY OF CAMS SEEM TO FIND THIS
IDEA POSSIBLE, BUT I ADMITTEDLY HAVE MY DOUBTS.
AFOREMENTIONED UNIDIRECTIONAL FLOW WILL BE A BIG PLAYER IN ANY
POTENTIAL CONVECTIVE EVOLUTION. HODOGRAPH SHAPE THIS EVENING WILL
LARGELY BE LINEAR, AND AS SUCH, WHILE THIS DOES EVENTUALLY FAVOR AN
OUTFLOW DOMINANT MULTICELLULAR / LINEAR MODE... SHOULD BE NOTED THAT
UPON CONVECTIVE INITIATION (WHEN STORMS ARE MOST DISCRETE), THIS DOES
FAVOR SPLITTING CELLS... WITH POTENTIAL FOR AN INITIAL LEFT MOVER
DOMINANT REGIME BEFORE TRANSITIONING INTO A LINEAR MODE WITH TIME...
AND SELECT CAMS HAVE THIS DOWN TO A TEE ACROSS THE NW LOWER
SHORELINE, PERHAPS SCRAPING THE VERY SOUTHERN REACHES OF MACKINAC
COUNTY... AS SUCH, THERE IS POTENTIAL FOR AN INTIAL HAIL DOMINANT
SEVERE THREAT ACROSS THE AFOREMENTIONED REGIONS BEFORE TRANSITIONING
TO A LINEAR, MORE WIND / OUTFLOW DOMINANT MODE THIS EVENING. SHOULD
NOTE... WE PROBABLY ONLY ACHIEVE THE MOST MARGINAL OF SEVERE
CONDITIONS AT BEST IF WE CAN HOLD ONTO PROGGED INSTABILITY TRENDS...
BUT IN THE EVENT WE TREND MORE DOWNWARD WITH INSTABILITY, THE THREAT
MAY BECOME MUCH MORE MUTED. NONETHELESS, ENOUGH IS THERE FOR SPC TO
EXPAND THE INHERITED DAY 1 MARGINAL RISK (1/5) ACROSS ALL OF
NORTHERN LOWER, BUTTING UP RIGHT AGAINST EASTERN UPPER. PRIMARY
HIGHLIGHTED HAZARD IS DAMAGING WIND GUSTS (5%), THOUGH IN THIS
MORNING'S MOST RECENT OUTLOOK, A 5% HAIL RISK HAS BEEN INTRODUCED TO
NW LOWER (GT BAY AND SOUTH), CUTTING OFF TO THE EAST ROUGHLY AT I-75
/ US 127... WHICH MATCHES WELL WITH A MAJORITY OF EVENING /
OVERNIGHT CONVECTIVE EPISODES... MOST ROBUST WEST, A BIT MORE
ISOLATED / WEAKER EAST.
FINAL PIECE OF THE PUZZLE IS HYDRO BASED CONCERNS. RECENT DRIER
WEATHER HAS ALLOWED OUR SOIL TO REVERT BACK TO ITS MORE NORMAL
POROUS SANDY CHARACTER... BUT WITH AN INCREASINGLY MOIST PROFILE
DURING THE FRONTAL PASSAGE, COUPLED WITH SOME BORDERLINE ECHO
TRAINING POTENTIAL (UNIDIRECTIONAL FLOW!) WITHIN PWATS SWELLING
CLOSER TO 1.50, IN THE EVENT REPEATED STORMS CAN MANIFEST, SUPPOSE
THERE IS POTENTIAL FOR SOME LOCALIZED HEAVY RAINFALL TOTALS. IN
PARTICULAR FOCUS BY CAMS IS THE NW LOWER CORRIDOR, INCLUDING THE
GRAND TRAVERSE BAY / TVC AREA, WHICH HAS A HANDFUL OF CAMS LAYING
DOWN A STRIP OF QUICK 1.50-2.50"+ OF RAIN. PENDING ON HOW QUICKLY
THIS CAN OCCUR (AND TO WHAT EXTENT), SUPPOSE THERE COULD BE A QUIET
FLOOD CONCERN, ESPECIALLY IF THIS CAN MANIFEST OVER THE TRAVERSE
CITY URBAN CORRIDOR... WITH MORE STRATIFORM / ISOLATED CONVECTIVE
MODES DRIVING LOWER RAINFALL TOTALS THE FARTHER EAST ONE GOES ACROSS
NORTHERN LOWER.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 133 PM EDT TUE AUG 18 2026
-SHRA AND -TSRA WILL SWEEP ACROSS ALL TAF SITES THIS EVENING,
RESULTING IN TEMPORARY REDUCTIONS IN CIG'S AND VSBY'S. MAINLY
VFR WITH PERIODS OF MVFR WILL PERSIST BETWEEN 1822 TO 1903Z
TONIGHT FOLLOWED BY VCSH AND PATCHY BR OVERNIGHT. WINDS VEER TO
THE NNW WEDNESDAY WITH SKC EXPECTED THROUGH THE REMAINDER OF
THE FORECAST PERIOD.
APX WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR LHZ345.
SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR LHZ346.
SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR LMZ323-
342-344>346.
DISCUSSION...HAD
AVIATION...SJC
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