SOUTHEAST ARIZONA FORECAST DISCUSSION
NWS TUCSON AZ
AFDTUS 210 AM MST THU JAN 30 2003
.SYNOPSIS...STRONG HIGH PRESSURE WILL REMAIN OVER THE DESERT STATES
INTO SATURDAY...PROVIDING DRY WEATHER AND NEAR RECORD HIGH
TEMPERATURES. A RATHER STRONG BUT DRY COLD FRONT WILL THEN SWEEP
ACROSS THE REGION SUNDAY MORNING...BRINGING WITH IT A ROUND OF GUSTY
WINDS AND MORE SEASONABLE TEMPERATURES. THE COOLER TEMPERATURES WILL
THEN CONTINUE FOR THE REST OF THE UPCOMING WEEK.
.DISCUSSION...MORE RECORDS IN TROUBLE TODAY AS WEAK DOWNSLOPE E FLOW
SETS UP. THIS WILL NOT ONLY GIVE US THE WARMEST TEMPS OF JAN SO FAR,
BUT IT WILL ALSO SOLIDIFY OUR 2ND WARMEST JAN ON RECORD AT KTUS.
WE'LL TAKE A QUICK PEEK AT THE 06Z MAV GUIDANCE WHEN IT ARRIVES, BUT
I SUSPECT BASED ON 850-700MB THICKNESSES WE MAY STILL BE A HAIR COLD
IN A FEW SPOTS. NORMALLY I WOULDNT QUIBBLE OVER 1-2F, BUT SINCE
WE'RE CLOSE TO RECORDS WILL FINE-TUNE IF NEEDED BEFORE PRESS TIME.
LATEST MODEL SUITE CONTINUES TO SHOW THAT THE SYSTEM NEAR 40N/145W
WILL DIG INTO THE SOUTHERN GREAT BASIN AND MAY BRIEFLY CLOSE OFF AS
THE MEAN RIDGE AMPLIFIES ALONG 130W. GFS HAS BEEN DOING ITS TYPICAL
FLIP-FLOP ON TIMING/STRENGTH WHILE THE UKMET/ECMWF REMAIN
CONSISTENT, AND LATEST ETA SEEMS TO BE HEADING IN THE UKMET/ECMWF
DIRECTION. THE 00Z GFS HAS TRENDED STRONGER, BUT EYEBALLING WATER
VAPOR IMAGERY AND ACARS DATA IT'S STILL PROBABLY TOO WEAK. THE
UPSHOT IS THAT EVEN THE WEAK-ISH GFS HAS SLOWED IT DOWN ABOUT 6HRS.
THAT NOT ONLY MEANS ANOTHER NEAR-RECORD DAY SAT, BUT ALSO SPELLS
POTENTIAL WIND PROBLEMS ON SUN AS THE TIGHTEST PRESSURE AND THERMAL
GRADIENT AFFECTS THE E CWA JUST BEFORE PEAK HEATING. IF THE UKMET
STRENGTH VERIFIES, WE'RE HEADING TOWARD WIND ADVISORIES AND BLOWING
DUST PROBLEMS FOR THE E CWA. I'M STILL BANKING THAT THE COLD
ADVECTION WILL BEAT OUT THE TIGHTEST GRADIENT FROM KTUS W, BUT
FUTURE SHIFTS WILL HAVE TO WATCH. WE'LL BUMP UP THE WIND WORDING IN
ZONES 19/30/35 FOR SUN, AND INCLUDE THE WIND/BLOWING DUST THREAT IN
OUR HWO. OTHERWISE, PREVIOUS SHIFTS HAVE ALREADY ADJUSTED TO THE
SOMEWHAT SLOWER TIMING IN TERMS OF CLOUD COVER AND TEMPS, SO WE'LL
LET THOSE DETAILS RIDE.
AS HAS BEEN MENTIONED BY THE PAST FEW DISCUSSIONS, EXTENDED PORTION
OF THE FORECAST IS GETTING MORE UNCERTAIN. ESSENTIALLY THE VERY
STABLE 4 WAVE PATTERN WE'VE BEEN IN SINCE EARLY JAN IS BREAKING DOWN
INTO CHAOTIC SPLIT FLOW. THIS SEEMS TO BE CAUSED, AT LEAST
PARTIALLY, BY A POLARITY SHIFT IN THE NORTH ATLANTIC OSCILLATION
(FROM WEAKLY NEGATIVE TO MODERATELY POSITIVE), WHILE THE POSITIVE
PNA PATTERN REMAINS FIRMLY ENTRENCHED. MODELS ARE GOING TO HAVE A
HARD TIME ADJUSTING TO THIS, ESPECIALLY WITH SUCH A STRONG RIDGE
ALONG 130W EITHER ALLOWING STRONG SYSTEMS TO DROP DOWN THE FRONT
SIDE, OR PIECES OF ENERGY TO BREAK UNDERNEATH AS THE SUBTROPICAL JET
BECOME ACTIVE. THE OLD ADAGE "WHEN IN A DROUGHT..." CERTAINLY
APPLIES HERE, BUT AT THE VERY LEAST THE CONSENSUS IS THAT WE'RE
GOING TO HAVE MORE TYPICAL LATE WINTER WEATHER NEXT WEEK WITH AT
LEAST SOME CLOUDS AND MORE SEASONABLE TEMPS. CURRENT EXTENDED HAS
THIS HANDLED VERY WELL. PYTLAK
.TWC...NONE.
AREA FORECAST DISCUSSION
NWS NORTHERN INDIANA
AFDFWA 235 AM EST FRI JAN 31 2003
SHORT TERM DISCUSSION...
FORECAST PROBLEM IS ONSET OF PRECIPITATION TODAY...ITS TYPE AT
BEGINNING AND AMOUNTS. THEN PROBLEMS FOCUS ON WARM UP BEING PROGGED
FOR SATURDAY THROUGH MONDAY AHEAD OF NEXT POTENT SYSTEM. MODELS IN
VERY GOOD AGREEMENT FOR TODAY. WATER VAPOR SHOWS SEVERAL SHORT
WAVES/VORT MAX CENTERS MOVING THROUGH PLAINS. MODELS ACTUALLY DO A
VERY GOOD JOB DEPICTING THE INDIVIDUAL FEATURES. SOUTHERN MOST VORT
CENTER SHOULD CONTINUE TO DIVE SOUTH AND AID IN CARVING OUT A SHARP
TROF TODAY OVER LOWER GREAT LAKES. WARM AIR ADVECTION AND SOUTHWEST
FLOW AHEAD OF THIS DEVELOPING TROF IS AIDING IN PRECIPITATION
DEVELOPMENT ACROSS IA/MO/NE/KS REGION. THIS PRECIPITATION...
CURRENTLY IN THE FORM OF RAIN WITH 850MB TEMPERATURES PLUS 2C TO
PLUS 9C...WILL CONTINUE TO MOVE EASTWARD THIS MORNING AND SATURATE
OUR LOWER LEVELS BY THIS AFTERNOON. INITIALLY THIS MORNING...LOWER
LEVELS VERY DRY WITH A WARM POCKET ABOVE 0C FROM JUST BELOW 950MB TO
JUST ABOVE 850MB. ACARS DATA CONFIRMS THIS WARM AIR. MODEL SOUNDINGS
ALL AGREE ON QUICKLY ELIMINATING THIS WARM AREA AS DYNAMIC AND
EVAPORATIVE COOLING OCCUR WITH SATURATION. STILL SOME CONCERN THAT
ANY INITIAL/FAST SATURATION COULD STILL YIELD A BRIEF PERIOD OF
LIGHT FREEZING RAIN...UNTIL WARM POCKET IS ELIMINATED DURING THE
EARLY AFTERNOON HOURS. PLAN TO CONTINUE A MENTION OF BRIEF AND LIGHT
FREEZING RAIN...THEN ALL SNOW. GENERAL ACCUMULATIONS OF 2 INCHES
LOOK GOOD...BUT AS WITH LAST SYSTEM...ONCE SATURATION OCCURS...SOME
MESOSCALE BANDING COULD YIELD SOME HIGHER AMOUNTS. 850MB...700MB
AND EVEN 500MB LOWS TRY TO BECOME CLOSED FOR A FEW HOURS...
ESPECIALLY ON LATEST GFS. FORECAST TECHNIQUES VARY BUT ALL YIELD
SOME MAX AMOUNTS OF 3 TO 5 INCHES...BUT THIS WOULD BE FOR A 12 HOUR
PERIOD. ISENTROPIC LIFT IS MAXIMIZED FOR MAINLY A 6 HOUR WINDOW AND
PART OF THAT IS BEFORE SATURATION. COOK AND MAGIC CHART METHODS
YIELD 4 TO 5 INCHES. DUE TO LESS THAN FAVORABLE TIME WINDOW AFTER
SATURATION...LACK OF GULF MOISTURE INFLUX AND GENERALLY AN OPEN WAVE
SYSTEM...PLAN TO CUT THESE AMOUNTS BACK BUT WL ADJUST CURRENT
AMOUNTS UP TO INCLUDE 3 INCHES. NO HEADLINES PLANNED.
MODELS AGAIN AGREE ON WARM UP FOR SATURDAY INTO SUNDAY AHEAD OF NEXT
SYSTEM THAT IS LOOKING POTENT. 850MB TEMPERATURES PROGGED TO RISE TO
BETWEEN PLUS 5 AND PLUS 10C ACROSS COUNTY WARNING FORECAST
AREA...CWFA. ETA HAS RELATIVELY LIGHT SURFACE WINDS...AND WITH
FROZEN GROUND AND MELTING SNOW PACK...FOG LOOKS LIKE A GOOD BET FOR
SATURDAY NIGHT AND SUNDAY. BELIEVE ETA IS TRYING TO MODEL THIS WITH
GREATER THAN 90 PERCENT RELATIVE HUMIDITIES IN THE LOWEST LEVELS
SATURDAY NIGHT AND SUNDAY. ETA IS ALSO KEEPING LOW LEVEL
TEMPERATURES MUCH COOLER THAN GFS. FOR NOW...WILL HAVE A COMPROMISE
BETWEEN THESE MODEL SOLUTIONS BUT LEANING TOWARD A COOLER BOUNDARY
LAYER WITH FOG AS WARM AIR ADVECTIONS STRENGTHENS THE INVERSION AND
FROZEN GROUND KEEPS SURFACE TEMPERATURES COOL. THIS COULD HAVE
SIGNIFICANT IMPACTS ON PRECIPITATION TYPE FOR MONDAY.
EXTENDED DISCUSSION...
AS ALREADY NOTED...SOME CONCERN SETTING UP FOR MONDAY AS 850 MB
TEMPS WELL ABOVE FREEZING...BUT SFC TEMPS...SUN NGT INTO EARLY
MONDAY WILL LIKELY BE AT OR BELOW FREEZING. TEMPS COULD VERY WELL
RISE ABOVE FREEZING DURING THE DAY...BUT WITH THE INVERSION...COULD
BE A TRICKY AND MESSY MONDAY. LATER FORECASTS WILL HAVE TO CLOSELY
WATCH THIS TREND. AFTER A BRIEF MIX...TRANSITION TO SNOW SHOULD
HAPPEN MONDAY NIGHT...WITH LINGERING SNOW ON TUESDAY. LAKE EFFECT
POTENTIAL WILL HAVE TO BE WATCHED...BUT DIFFERENTIALS REMAIN IN THE
LOWER TO MIDDLE TEENS INITIALLY. SKIES WILL CLEAR OUT ON WEDS AS
RIDGING TAKES PLACE ACROSS THE REGION. WEAK SYSTEM WILL MOVE IN ON
THURSDAY...WITH A CHC OF SNOW. TEMP ABOVE NORMAL THROUGH MONDAY
NGT...THEN NEAR NORMAL CONDITIONS EXPECTED.
.IWX...
IN...NONE.
MI...NONE.
OH...NONE.
LASHLEY/FISHER