Area Forecast Discussion
Issued by NWS Hastings, NE

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000
FXUS63 KGID 180948
AFDGID

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HASTINGS NE
348 AM CST THU DEC 18 2014

.SHORT TERM...(TODAY AND TONIGHT)

SHORT TERM DISCUSSION WILL BE ISSUED WITHIN ONE HOUR.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 348 AM CST THU DEC 18 2014

GUIDANCE SUGGESTS SEVERAL UPPER TROPOSPHERIC SHORT WAVES WILL BE
NOTED MOVING OVER THE CENTRAL PLAINS DURING THE LONG TERM FORECAST
PERIOD. THE FIRST SHORT WAVE IS EXPECTED TO EXIST OVER THE CENTRAL
HIGH PLAINS TO START THE LONG TERM FORECAST PERIOD AT 12Z
FRIDAY...WITH THIS SHORT WAVE THEN EXPECTED TO CLEAR THE CENTRAL
PLAINS DURING THE DAY FRIDAY. A SECOND UPPER TROPOSPHERIC SHORT
WAVE IS EXPECTED TO CLEAR OUR AREA SATURDAY INTO SATURDAY
NIGHT...WITH ONE MORE SHORT WAVE THEN EXPECTED SUNDAY NIGHT INTO
MONDAY.

STARTING WITH FRIDAY MORNING...GUIDANCE FROM THE NAM AND
OPERATIONAL GFS SUGGEST 0-0.5KM RELATIVE HUMIDITY VALUES IN EXCESS
OF 90%...ALONG WITH 0-0.5KM BULK SHEAR NEAR OF JUST ABOVE
10KTS...AS WELL AS SOME SUBTLE LIFT AHEAD OF THE FIRST OF THE
AFOREMENTIONED UPPER TROPOSPHERIC SHORT WAVES...MAY PROMOTE
PERIODIC LIGHT FREEZING DRIZZLE ACROSS EASTERN PORTIONS OF THE CWA
THROUGH LATE MORNING. IT IS WORTH MENTIONING THAT FORECAST
PROXIMITY SOUNDINGS FROM ACROSS OUR CWA...PER THE NAM AND
OPERATIONAL GFS...SUGGEST THE LAYER OF SATURATION NEAR THE SURFACE
WILL BE VERY THIN AND BASED ON THIS DATA...IT SHOULDNT TAKE LONG
TO MIX OUT THE SATURATED LAYER POST- SUNRISE. BUT NONETHELESS
THERE IS STILL AN OPPORTUNITY FOR FREEZING DRIZZLE FOR AT LEAST A
TIME FRIDAY MORNING AND GIVEN THIS...WILL GO AHEAD AND CONTINUE
SUCH WORDING IN THE FORECAST THROUGH 15Z FRIDAY.

OF THE THREE AFOREMENTIONED SHORT WAVES...THE OPERATIONAL GFS AND
EC BOTH SUGGEST THE THIRD WAVE...SUNDAY NIGHT INTO MONDAY...WILL
BE THE STRONGEST AS IT CLEARS THE REGION. IN FACT...DPVA AND UPPER
TROPOSPHERIC THERMAL ADVECTION...AS WELL AS TROPOSPHERIC
MOISTURE...IN ASSOCIATION WITH THE FIRST TWO WAVES APPEAR SO
MEAGER THAT THE PROBABILITY OF MEASURABLE PRECIPITATION PRODUCTION
WITH EITHER OF THE TWO FIRST WAVES SEEMS VERY LOW AND AS A
RESULT...WENT AHEAD WITH A PRECIPITATION-FREE FORECAST FRIDAY
THROUGH THE DAY SUNDAY.

HEADING INTO SUNDAY NIGHT...GUIDANCE SUGGESTS BOTH DPVA AND UPPER
TROPOSPHERIC THERMAL ADVECTION WILL INCREASE ENOUGH FOR
PRECIPITATION PRODUCTION ACROSS PORTIONS OF THE
REGION...ESPECIALLY ACROSS NORTHERN AND EASTERN NEBRASKA AS THE
THIRD SHORT WAVE APPROACHES. GIVEN THIS...WENT AHEAD WITH ~20%
POPS ACROSS EXTREME EAST/NORTHEASTERN PORTIONS OF THE CWA SUNDAY
NIGHT INTO MONDAY. ALTHOUGH IT APPEARS THE UPPER TROPOSPHERIC
SHORT WAVE WILL CLEAR THE REGION DURING THE DAY MONDAY...THERE ARE
ALSO INDICATIONS...FROM THE OPERATIONAL GFS AND EC...THAT THE
LEFT-FRONT QUADRANT OF A ~150KT UPPER TROPOSPHERIC JET STREAK WILL
DEVELOP OVER THE CENTRAL PLAINS MONDAY NIGHT INTO TUESDAY...THUS
PROVIDING ADDITIONAL CHANCES FOR PRECIPITATION PRODUCTION. GIVEN
THIS...WENT AHEAD WITH ~20% POPS ACROSS NORTHERN AND EASTERN
PORTIONS OF OUR CWA MONDAY NIGHT INTO TUESDAY AS WELL.

FORECAST PROXIMITY SOUNDINGS FROM ACROSS THE OUR NORTHERN AND
EASTERN CWA...PER THE OPERATIONAL GFS AND EC...SUGGEST
PRECIPITATION TYPE WILL VARY BETWEEN LIGHT RAIN AND LIGHT SNOW
MONDAY THROUGH TUESDAY. IT IS WORTH MENTIONING THAT PRECIPITATION
TYPE WILL NEED TO BE CLOSELY MONITORED EARLY MONDAY MORNING JUST
PRIOR TO SUNRISE AS THIS IS A TIME WHEN FORECAST PROXIMITY
SOUNDINGS FROM THE OPERATIONAL GFS AND EC BOTH SUGGEST A STRONG
ELEVATED WARM LAYER WILL CONTINUE TO PROMOTE LIQUID PRECIPITATION
AS SURFACE TEMPERATURE READINGS APPROACH THE FREEZING MARK. AT
THIS TIME THE CURRENT FORECAST CALLS FOR SURFACE TEMPERATURE
READINGS TO REMAIN JUST ABOVE FREEZING THROUGH SUNRISE MONDAY BUT
AGAIN...THIS WILL NEED TO BE MONITORED AS ANY DECREASE IN THE LOWS
FOR MONDAY MORNING COULD PRESENT THE POSSIBILITY FOR PERIODIC
LIGHT FREEZING RAIN ACROSS OUR NORTHEAST FOR A FEW HOURS MONDAY
MORNING.

A PERSISTENT SOUTHERLY COMPONENT TO THE BOUNDARY-LAYER WIND FIELD
AND RESULTANT THERMAL ADVECTION SHOULD PROMOTE A GENERAL WARMING
TREND FRIDAY THROUGH MONDAY. AFTERNOON HIGHS IN THE 30S AND LOW
40S ON FRIDAY ARE CURRENTLY EXPECTED TO RISE INTO THE 40S AND LOW
50S ACROSS THE CWA BY MONDAY...WHILE OVERNIGHT LOWS START IN THE
TEENS AND LOW 20S FRIDAY NIGHT BUT SHOULD EVENTUALLY CLIMB INTO
THE UPPER 20S AND LOWER 30S BY SUNDAY NIGHT. THE PASSAGE OF A
BOUNDARY-LAYER BAROCLINIC ZONE MONDAY...IN ASSOCIATION WITH THE
UPPER TROPOSPHERIC SHORT WAVE ALSO CLEARING THE AREA...SHOULD THEN
ALLOW FOR A SOMEWHAT COOLER FINISH TO THE FORECAST PERIOD...WITH
HIGHS IN THE MID 30S TO LOW 40S AND LOWS IN THE BACK INTO THE 20S
BY NEXT WEDNESDAY.

&&

.AVIATION...(FOR THE 06Z KGRI/KEAR TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1152 PM CST WED DEC 17 2014

YET AGAIN...ANOTHER TAF PERIOD WITH A SOMEWHAT CHALLENGING/TRICKY
FORECAST REGARDING MAINLY CEILING TRENDS...BUT POSSIBLY VISIBILITY
AS WELL. ON TOP OF THIS...AT LEAST A BRIEF PERIOD OF LIGHT SNOW IS
LIKELY RIGHT AWAY DURING THESE FIRST 6 HOURS EARLY THIS
MORNING...WITH AMOUNTS LIKELY AVERAGING LESS THAN ONE-HALF INCH.
ALTHOUGH NOT INDICATED IN THE TAFS DUE TO LACK OF CONFIDENCE IN
COVERAGE/OCCURRENCE...A BRIEF PERIOD OF LIGHT FREEZING DRIZZLE
CANNOT BE RULED AS WELL. SO...THE BOTTOM LINE IS THAT CEILING-
WISE...DESPITE SOME MODELS/GUIDANCE SUGGESTING A RETURN TO
PREVAILING VFR THROUGH MUCH OF THE LATTER HALF OF THE
PERIOD...HAVE INSTEAD MAINTAINED A MORE PESSIMISTIC ROUTE AS
SUGGESTED BY OTHER MODELS/GUIDANCE AND THE PREVIOUS
FORECAST...WITH A COMBINATION OF MVFR/IFR CEILING PERSISTING
THROUGH NEARLY THE ENTIRE PERIOD. VISIBILITY WISE...ALTHOUGH SOME
LIGHT FOG COULD BECOME A FACTOR...FOR NOW HAVE ONLY INDICATED SUB-
VFR CONDITIONS IN ASSOCIATION WITH ANY FALLING SNOW DURING THE
FIRST SEVERAL HOURS. FORTUNATELY...SURFACE WINDS WILL NOT BE A
MAJOR AVIATION ISSUE THROUGH THE PERIOD...WITH SUSTAINED SPEEDS
AVERAGING UNDER 10KT THROUGHOUT...AS DIRECTION TRANSITIONS FROM
EASTERLY TO SOUTHERLY.


&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...WINTER WEATHER ADVISORY UNTIL 9 AM CST THIS MORNING FOR KSZ007-
     018-019.

&&

$$

LONG TERM...BRYANT
AVIATION...PFANNKUCH


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