Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 010846
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
346 AM CDT SUN MAY 1 2016

FORECAST DISCUSSION FOR ROUTINE MORNING FORECAST ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND MONDAY
ISSUED AT 343 AM CDT SUN MAY 1 2016

OLD UPPER LOW OVER IOWA WILL WEAKEN AS IT MOVES EAST TOWARDS
SOUTHERN WISCONSIN TODAY. IT/S WEAK UPPER SUPPORT MAY PRODUCE SOME
LIGHT RAIN OR SPRINKLES OVER THE SOUTHERN THIRD OF THE AREA BUT
MOST AREAS WILL RECEIVE JUST A FEW HUNDREDTHS OF RAIN OR NOTHING.
EXPECT SOME CLEARING LATER TODAY BUT IT WILL BE SLOW. HIGHS TODAY
SHOULD BE A COUPLE OF DEGREES BELOW NORMAL AND COLDER YET NEAR
LAKE MICHIGAN.

SKIES SHOULD BECOME CLEAR OVER MOST AREAS TONIGHT AS A WEAK UPPER
RIDGE ARRIVES. SOME PATCHY FROST IS POSSIBLE ACROSS CENTRAL AND
EAST CENTRAL WISCONSIN BUT DO NOT THINK IT WILL BE SIGNIFICANT. A
FROST OR FREEZE IS LIKELY IN THE NORTH BUT THAT IS NOT UNUSUAL
THERE. LOWS TONIGHT SHOULD BE A FEW DEGREES BELOW NORMAL.

PARTLY SUNNY SKIES AND SEASONABLE TEMPERATURES ARE EXPECTED
MONDAY THOUGH A BRIEF SHOWER IS NOT OUT OF THE QUESTION LATER IN
THE DAY AS A WEAK UPPER TROUGH MOVES BY.

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY
ISSUED AT 343 AM CDT SUN MAY 1 2016

LONG-RANGE MODELS CONTINUE TO INDICATE AN INCREASINGLY AMPLIFIED/
BLOCKY PATTERN OVER THE CONUS NEXT WEEK. WHILE THE MODELS AGREE ON
TAKING AN EASTWARD MOVING SHORTWAVE TROUGH INTO THE WESTERN
CONUS...THEN CLOSING THIS TROUGH INTO A CLOSED UPPER LOW OVER THE
SW CONUS...THERE ARE STILL ISSUES WITH THE DEVELOPMENT OF THE
EASTERN CONUS UPPER TROUGH AND THE POTENTIAL/LOCATION OF THIS
TROUGH ALSO BECOMING A CLOSED UPPER LOW. IF THIS EASTERN CONUS
UPPER SYSTEM OCCURS FARTHER WEST...THIS WOULD IMPACT OUR WEATHER
DURING THE EARLY TO MIDDLE PART OF THE WEEK. THIS IS THE MOST
CHALLENGING PART OF THE FORECAST WITH THE MOST QUESTIONS.
TEMPERATURES WILL BRIEFLY WARM AHEAD OF A COLD FRONT (TUE)...THEN
FALL TO BELOW NORMAL LEVELS ONCE AGAIN THROUGH THE END OF THE WORK
WEEK.

QUIET CONDITIONS ARE EXPECTED MONDAY NIGHT AS THE REGION TO RESIDE
ON THE NORTHERN EDGE OF A WEAK RIDGE OF HIGH PRESSURE. PARTLY
CLOUDY SKIES AND A LIGHT SW WIND WILL LEAD TO MIN TEMPERATURES IN
THE UPPER 30S TO AROUND 40 DEGREES NORTH...40-45 DEGREE RANGE
SOUTH. THE NEXT CHANCE OF SEEING SHOWERS/ISOLATED THUNDERSTORMS
ARRIVES TUESDAY AFTERNOON AS A SURFACE COLD FRONT/MID-LEVEL
SHORTWAVE TROUGH DROPS SOUTH OUT OF CANADA. MODELS HAVE COME
CLOSER IN TIMING THE COLD FRONT INTO NORTHERN WI BY 00Z
WEDNESDAY...THUS POPS TO INCREASE FROM NORTH TO SOUTH DURING THE
AFTERNOON HOURS. THERE IS GOOD LIFT EVIDENT BETWEEN THE COLD FRONT
AND THE LEFT EXIT REGION OF THE UPPER JET...WITH INCREASED
INSTABILITY WITH LI`S DOWN TO AROUND ZERO AND STEEPENING MID-LEVEL
LAPSE RATES. WOULD LIKE TO SEE A LITTLE DEEPER MOISTURE PRESENT
WHEN THE FRONT ARRIVES...HOWEVER THE LIFT AND FORCING APPEAR
SUFFICIENT TO AT LEAST MENTION ISOLATED THUNDERSTORMS. PRE-FRONTAL
WARMING SHOULD PUSH MAX TEMPERATURES INTO THE MID TO UPPER 60S
NORTH...UPPER 60S TO AROUND 70 DEGREES SOUTH (COOLER LAKESIDE).

THE COLD FRONT/SHORTWAVE TROUGH SWEEP SOUTHWARD THROUGH THE REST
OF WI TUESDAY EVENING AND PUSH SOUTH INTO IL OVERNIGHT. BEHIND
THIS SYSTEM...A CYCLONIC FLOW WILL BE LEFT OVER WI AS THE MAIN
SHORTWAVE TROUGH BEGINS TO TAKE SHAPE OVER THE GREAT LAKES. WHILE
THE BULK OF THE SHOWERS/ISOLATED STORMS WILL END TUESDAY
EVENING...CANNOT RULE OUR SOME LINGERING LIGHT SHOWERS...
ESPECIALLY OVER NORTHERN WI WHERE CAA/NORTH WINDS COULD ACTUALLY
BRING LAKE ENHANCEMENT FROM SUPERIOR. MIN TEMPERATURES TO RANGE
FROM THE MID TO UPPER 30S NORTH...TO MAINLY LOWER 40S SOUTH. THIS
DEVELOPING UPPER TROUGH IS FORECAST TO DIG SOUTHWARD TOWARD THE
OHIO RIVER/TN VALLEYS ON WEDNESDAY...THEREBY KEEPING A COOLER
CYCLONIC FLOW OVER WI. WE WILL HAVE TO WATCH FOR THE POTENTIAL OF
BUILDING CUMULUS DURING DAYTIME HEATING AND THE CHANCE FOR A POP-
UP SHOWER...ESPECIALLY OVER EASTERN SECTIONS WHERE THE AIR ALOFT
WILL BE COOLER. PREVIOUS FORECAST ALREADY HAD A MINIMAL POP IN THE
EAST AND WILL NOT MAKE ANY CHANGES. WEDNESDAY WILL ALSO BE
NOTICEABLY COOLER (COMPARED TO TUESDAY) WITH MAX TEMPERATURES ONLY
IN THE UPPER 40S TO LOWER 50S FAR NORTH...TO THE UPPER 50S OVER
PARTS OF CENTRAL WI.

THE HIGHLY-AMPLIFED MIEAN FLOW ACROSS THE CONUS TO BE IN PLACE BY
NEXT THURSDAY WITH A DEEP UPPER TROUGH ALONG THE WEST COAST...AN
UPPER RIDGE OVER THE EASTERN ROCKIES AND THE AFOREMENTIONED UPPER
TROUGH OVER THE EASTERN CONUS. WHILE THE MODELS STILL DISAGREE TO
A CERTAIN EXTENT WHERE THE EASTERN TROUGH WILL RESIDE...THE
CYCLONIC FLOW OVER THE WESTERN GREAT LAKES IS EXPECTED TO WEAKEN A
BIT. THUS...WHILE DAYTIME FAIR WEATHER CUMULUS IS EXPECTED...DO
NOT ANTICIPATE ANY SHOWER DEVELOPMENT ON THURSDAY. MAX
TEMPERATURES SHOULD WARM A LITTLE COMPARED TO WEDNESDAY WITH
READINGS IN THE MID TO UPPER 50S NORTH/LAKESHORE...UPPER 50S TO
LOWER 60S SOUTH.

AS THE WESTERN CONUS UPPER TROUGH CLOSED INTO AN UPPER LOW NEAR CA
THURSDAY NIGHT INTO FRIDAY...THE UPPER RIDGE IS FORECAST TO SHIFT
SLIGHTLY TO THE EAST INTO THE PLAINS. MEANWHILE AT THE SURFACE...
A BROAD AREA OF HIGH PRESSURE TO EXTEND FROM WESTERN ONTARIO SOUTH
ALL THE WAY TO THE GULF OF MEXICO. ANTICIPATE MORE SUNSHINE ACROSS
THE FORECAST AREA WITH TEMPERATURES CONTINUING TO SLOWLY MODIFY
CLOSER TO NORMAL FOR EARLY MAY.

ONLY CHANGE OF NOTE HEADED INTO NEXT WEEKEND WILL BE THE SLIGHT
WEAKENING OF THE PLAINS UPPER RIDGE IN RESPONSE TO THE MOVEMENT OF
A COLD FRONT/VERY WEAK SHORTWAVE TROUGH ACROSS THE CANADIAN
PRAIRIES INTO NORTHERN SECTIONS OF ND AND MN. HIGH PRESSURE SHOULD
STILL BE IN CONTROL OF OUR WEATHER THROUGH SATURDAY...SO DRY
CONDITIONS WILL HOLD WITH MAX TEMPERATURES WARMING INTO THE UPPER
60S TO LOWER 70S AWAY FROM THE COOLER LAKE AND BAY.
&&

.AVIATION...FOR 06Z TAF ISSUANCE
ISSUED AT 1047 PM CDT SAT APR 30 2016

MAINLY VFR CIGS AND VSBYS EXPECTED TONIGHT INTO SUNDAY.
TIGHTENING PRESSURE GRADIENT IN THE BOUNDARY LAYER WILL PRODUCE A
PERIOD OF LLWS CONDITIONS OVERNIGHT FOR THE TAF SITES. THIS EVEN
INCLUDES RHI FOR A FEW HOURS. LLWS CONDITIONS BEING CREATED BY A
STORM SYSTEM TRACKING OVER THE MID MISSISSIPPI VALLEY REGION AND
HIGH PRESSURE EXTENDING INTO THE NORTHERN GREAT LAKES. A DECREASING
BAND OF RAIN OVER THE SOUTH HALF OF THE STATE WILL DEPART LATE
SUNDAY MORNING. PATCHES OF MVFR CIGS MAY ALSO EXTEND INTO AREAS
SOUTH OF HIGHWAY 29 OVERNIGHT BEFORE DEPARTING LATER SUNDAY.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....RDM
LONG TERM......KALLAS
AVIATION.......TDH



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