Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 282305
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
705 PM EDT FRI AUG 28 2015

.SYNOPSIS...
ISSUED AT 638 PM EDT FRI AUG 28 2015

LOW PRESSURE OVER IOWA WILL WEAKEN AS IT MOVES SLOWLY EAST THIS
WEEKEND... BUT STILL SHOULD CAUSE SCATTERED SHOWERS AND POSSIBLY A
FEW THUNDERSTORMS IN OUR AREA SATURDAY AND SUNDAY. LOWS TONIGHT
WILL BE IN THE UPPER 50S AND LOWER 60S... WITH HIGHS SATURDAY IN
THE UPPER 70S AND LOWER 80S.

&&

.UPDATE...
ISSUED AT 638 PM EDT FRI AUG 28 2015

CIRRUS SHIELD SPREADING SLOWLY ACROSS THE AREA THIS EVE MORE
EXTENSIVE THAN SUGGESTED BY GOING GRIDS AND GIVEN NEARLY SOLID
HIGH DECK UPSTREAM ACROSS CENTRAL/NRN IL HAVE MADE UPWARD
ADJUSTMENTS TO SKY GRIDS...ESPECIALLY NW HALF OF CWA.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 413 PM EDT FRI AUG 28 2015

LOW PRESSURE SYSTEM WILL BRING RAIN TO THE AREA TONIGHT AND
SATURDAY

MODERATE TO HEAVY PRECIPITATION OBSERVED OVER IA/SE MN/WISCONSIN
THIS AFTERNOON IS ASSOCIATED WITH UPPER LEVEL DIVERGENCE IN THE
RIGHT ENTRANCE REGION OF A JET STREAK PASSING THROUGH THE GREAT
LAKES. IN THE MID LEVELS...THERE IS A POTENT 500MB VORT MAX/PV
ANOMALY AND BROAD REGION OF WAA/STRONG ISENTROPIC ASCENT.
PRECIPITATION IS MAINLY AHEAD OF THE WARM FRONT...WITH THE SURFACE
LOW OVER IA. THIS SYSTEM WILL DRIFT EASTWARD THROUGH THE SHORT
TERM...AND LEAD TO PRECIPITATION CHANCES OVER THE CWA TONIGHT AND
SATURDAY.

HOWEVER...THE 500MB VORT MAX WEAKENS AND LIFTS NORTHWARD INTO LOWER
MI TONIGHT AND SATURDAY AS IT ENCOUNTERS THE HIGH PRESSURE RIDGE
ANCHORED OVER THE ATLANTIC...AND FORCING FROM THE JET STREAK/UPPER
LEVEL DIVERGENCE SHIFTS NORTHWARD. THE AREA WILL BE UNDER WEAK WAA
TONIGHT...WITH THE WARM FRONT SHIFTING NORTHWARD INTO LOWER MI BY
21Z SUNDAY...BUT AS FORCING ALOFT DWINDLES BEST WAA DIES OFF TO THE
NORTHWEST. MOISTURE IS ALSO LIMITED...WITH PWATS AROUND 1.2
INCHES/RIGHT AROUND NORMAL. WITH FORCING MOVING NORTH AND DRY AIR IN
PLACE EARLIER ON...THINK THE PRECIPITATION WILL BE LIMITED TO THE
FAR NORTHWESTERN PORTIONS OF THE CWA TONIGHT. KEPT A MAJORITY OF THE
CWA DRY FOR NOW WITH THE EXCEPTION OF ISOLATED SHOWERS NEAR LAKE
MICHIGAN. WOULD NOT BE SURPRISED TO SEE SOME PATCHY FOG DEVELOP
LATER WITH INCREASING MOISTURE AND NEARLY CALM WINDS EXPECTED.

STRONGER MOISTURE TRANSPORT FROM THE GULF/ATLANTIC STATES DEVELOPS
WITH SOUTH-SOUTHEAST FLOW AROUND THE SFC HIGH TO THE SOUTHEAST AND
WITH THE APPROACHING SFC LOW TO THE WEST. BY SATURDAY AFTERNOON
PWATS CLIMB TO 120-140 PERCENT OF NORMAL AND DEWPOINTS RISE INTO THE
LOW TO MID 60S. THE SFC COLD FRONT IS FORECAST TO MOVE INTO IL/NW
INDIANA TOWARDS LATE SAT AFTERNOON EVENING...THOUGH FORCING ALOFT BY
THIS TIME IS WANING AND THE SURFACE LOW/NOW OVER LAKE MICHIGAN/ IS
WEAKENING. INSTABILITY IS DECENT IN OUR AREA...AND RANGES FROM 1500-
2500 J/KG MUCAPE BY LATE AFTERNOON...DEPENDING ON THE MODEL USED. 0-
6 KM SHEAR IS LACKING HOWEVER...ONLY AROUND 15-20 KNOTS IN THE
AFTERNOON. THUNDERSTORMS ARE DEFINITELY POSSIBLE...BUT UNLIKELY TO
BE SEVERE. SINCE MODELS VARY QUITE A BIT IN REGARDS TO EXACT
TIMING/PLACEMENT OF PRECIPITATION-AND GIVEN WEAKER FORCING/WEAKENING
TREND...HAVE LEFT HIGH-END CHANCE POPS FOR NOW ON
SATURDAY...ESPECIALLY TOWARDS THE AFTERNOON. KEPT THUNDERSTORMS
CONFINED TO THE AFTERNOON WHEN INSTABILITY IS GREATEST.

OTHERWISE...HIGH TEMPERATURES WILL RANGE FROM THE UPPER 70S TO THE
80S SATURDAY. LOWS TONIGHT WILL DIP INTO THE UPPER 50S AND LOW 60S.

&&

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 413 PM EDT FRI AUG 28 2015

AT THE BEGINNING OF THE PERIOD...AN UPPER LEVEL SHORT WAVE TROF WILL
MOVE ACROSS THE LOWER GREAT LAKES REGION BRINGING A MODERATE CHANCE
FOR PRECIPITATION SAT NIGHT INTO SUN. THE PRECIP WILL END WEST TO
EAST DURING THE DAY. AT THE BEGINNING OF NEXT WEEK...HEIGHTS WILL
INCREASE AS UPPER RIDGING BUILDS INTO THE REGION ALLOWING FOR HIGHER
HUMIDITY LEVELS AND WARMER TEMPS. MONDAY IS EXPECTED TO BE DRY
WITH PASSAGE OF THE UPPER LEVEL SHORT WAVE. THE EFFECTS FROM ERIKA
COULD BE FELT NEXT WEEK SO HAVE INTRODUCED LOW END POPS FOR
PRIMARILY AFTERNOON HOURS WED-FRI DUE WITH AN EXPECTED RETURN OF
HIGHER DEWPOINTS DURING THE WEEK. TEMPS DURING THE PERIOD WILL WARM
FROM THE UPPER 70/LOWER 80S SUN TO UPPER 80S BY THE END OF THE
WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 638 PM EDT FRI AUG 28 2015

VFR CONDITIONS SHOULD CONTINUE ACROSS NRN INDIANA TONIGHT WITH THE
PSBL EXCEPTION OF MVFR VSBYS IN BR TOWARD DAYBREAK. W-E ORIENTED
BOUNDARY AHEAD OF WK SFC LOW AND UPR LEVEL TROF APCHG FROM THE
W-NW EXPECTED TO RESULT IN SCT CONVECTION ACROSS OUR AREA SATURDAY
AFTN. NAM INSTABILITY ACROSS NRN INDIANA FOR SATURDAY APPEARS
OVERDONE BASED ON CONDITIONS UPSTREAM ATTM AND WEAKER INSTABILITY
PROGGED BY GFS PREFERRED... THUS JUST MENTIONED SHRA AT SBN IN
THIS TAF WITH POPS TOO LOW TO ADD TO FWA TAF ATTM.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

UPDATE...JT
SYNOPSIS...JT
SHORT TERM...MCD
LONG TERM...FRAZIER
AVIATION...JT


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