Area Forecast Discussion
Issued by NWS Tucson, AZ

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FXUS65 KTWC 211624
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
924 AM MST WED JAN 21 2015

.SYNOPSIS...A STORM SYSTEM PASSING EAST ACROSS THE STATE WILL
GENERATE SOME SHOWERS EAST AND NORTH OF TUCSON LATER TODAY INTO
TONIGHT.  A SECOND SYSTEM WILL DROP SOUTH ALONG THE NEW MEXICO
BORDER THURSDAY DRIVING MUCH COOLER AND DRIER AIR ACROSS THE AREA
THURSDAY INTO FRIDAY.  TEMPERATURES WILL WARM TO ABOVE NORMAL LEVELS
AGAIN OVER THE WEEKEND UNDER MOSTLY CLEAR SKIES...THEN ANOTHER STORM
SYSTEM MAY BRING SHOWERS TO THE REGION THE EARLY PART OF NEXT WEEK.

&&

.DISCUSSION...A SYSTEM WAS PASSING THROUGH ARIZONA WILL BRING A
FEW SHOWERS TO THE AREA TODAY. RADAR SHOWED SOME LIGHT SHOWERS OR
SPRINKLES ALREADY THIS MORNING. THE MAIN PRECIPITATION WILL BE LATER
THIS EVENING AND TONIGHT AS A SECONDARY SYSTEM DROPS SOUTH THROUGH
THE FOUR CORNERS REGION AND BRUSHES EASTERN ARIZONA. MOST OF THIS
SHOWER ACTIVITY WILL BE CONFINED TO AREAS NORTH AND EAST OF TUCSON.
THIS SECOND SYSTEM WILL ALSO USHER IN MUCH COLDER AIR RESULTING IN A
SIGNIFICANT DROP IN TEMPERATURES ON THURSDAY. AT ANY RATE...THE
CURRENT FORECAST LOOKED ON TRACK SO NO UPDATES NECESSARY THIS
MORNING. REFER TO THE ADDITIONAL SECTIONS IN THIS PRODUCT FOR MORE
DETAILS.

&&

.AVIATION...VALID THRU 22/18Z.
VFR CONDITIONS WILL PREVAIL THROUGH THE FORECAST PERIOD. CLOUD
CEILINGS WILL BE AROUND 10-15K FT AGL. SHOWERS WILL PRIMARILY BE
CONFINED TO THE PINALENO AND WHITE MOUNTAINS TODAY AND TONIGHT.
WINDS WILL INCREASE OUT OF THE SOUTHWEST AND BECOME WESTERLY THIS
AFTERNOON AT 10 TO 15 KTS WITH OCCASIONAL GUSTS TO 25 KTS WITH THE
STRONGEST WINDS OCCURRING SOUTH AND EAST OF KTUS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...A CHANCE OF RAIN AND MOUNTAIN SNOW SHOWERS WILL
EXIST TODAY THROUGH THURSDAY ACROSS AREAS TO THE NORTH AND EAST OF
TUCSON. BREEZY SOUTHWESTERLY WINDS WILL DEVELOP THIS
AFTERNOON...PRIMARILY SOUTH OF TUCSON. SLIGHTLY ABOVE NORMAL
TEMPERATURES TODAY WILL BE FOLLOWED BY A COOLING TREND WITH HIGHS
DROPPING TO ROUGHLY 4 TO 8 DEGREES BELOW NORMAL THURSDAY AND FRIDAY.
THEREAFTER...DRY CONDITIONS AND ANOTHER WARMING TREND ARE EXPECTED
THROUGH THE WEEKEND. A PERSISTENT EASTERLY WIND WILL SET UP THURSDAY
NIGHT AND INTO THE WEEKEND WITH LOCALLY GUSTY CONDITIONS NEAR
FAVORED MOUNTAIN GAPS.

&&

.PREV DISCUSSION...AN UPPER TROUGH WILL MOVE EAST ACROSS THE STATE
THROUGH THE DAY GENERATING SHOWERS OVER THE NORTHERN AND CENTRAL
PARTS OF THE STATE...PRIMARILY AFFECTING THE MOUNTAINS WELL
NORTHEAST OF TUCSON...ESPECIALLY THE WHITES THIS AFTERNOON AND EARLY
EVENING.  THE SOUTHWEST FLOW AND UPWARD MOTION IN ADVANCE OF THIS
SYSTEM IS EXPECTED TO MOISTEN THE AIR MASS ENOUGH ACROSS EASTERN
PORTIONS OF THE FORECAST AREA...LIKE COCHISE COUNTY...TO BRING ABOUT
A SMALL POSSIBILITY OF A SHOWER LATER TODAY.  WITH ALL THAT
SAID...BASICALLY ENDED UP WITH SLIGHT CHANCE POPS JUST NORTH AND
EAST OF TUCSON...WITH CHANCE POPS OVER THE PINALENO MTNS AND LIKELY
POPS OVER THE WHITES.  OVERALL...TEMPS ABOUT 5 DEG COOLER THAN
YESTERDAY ALTHOUGH THE CLOUD COVER WILL MAKE IT FEEL EVEN A BIT
COOLER.

THEN A SHORTWAVE TROUGH CURRENTLY OVER WESTERN MONTANA WILL DIVE
STRAIGHT SOUTH AS IT DEEPENS INTO A CLOSED LOW ALONG THE NORTHERN
AZ/NM BORDER BY THURSDAY MORNING.  THIS SYSTEM WILL CONTINUE MOVING
SSE THURSDAY ENDING UP OVER THE WESTERN PAN HANDLE OF TEXAS BY EARLY
FRIDAY MORNING.  WHILE THIS LOW WILL BE TOO FAR TO THE EAST TO
PROVIDE ANY PRECIPITATION IT WILL DRIVE COOLER AND MUCH DRIER AIR
ACROSS THE AREA ON BRISK NORTH TO NORTHEAST WINDS THURSDAY BECOMING
EAST FRIDAY.  HIGH TEMPERATURES THURSDAY WILL BE 10-15 DEG COOLER
THAN THIS AFTERNOON WHICH WILL BE ABOUT 6 DEG BELOW NORMAL.  THE
COOL AND DRY CONDITIONS WILL CONTINUE THROUGH FRIDAY.

FOR THE WEEKEND A REX BLOCK IS EXPECTED TO DEVELOP TO OUR WEST WITH
THE HIGH CENTERED OVER NORTHERN CALIFORNIA AND THE LOW WELL WEST OF
THE SOUTHERN TIP OF BAJA.  THIS WILL MAKE FOR AN INTERESTING WEATHER
PATTERN FOR OUR AREA AND WILL NEED TO WATCH HOW THIS DEVELOPS AS
THERE WILL BE A SHARP LINE BETWEEN THE MOISTURE HEADING NORTH AND
THE STRONG SUBSIDENCE ASSOCIATED WITH THE HIGH.  AT THIS TIME HAVE
KEPT THAT LINE NEAR OR JUST SOUTH OF THE MEXICAN BORDER SUNDAY AND
MONDAY ALTHOUGH IT IS POSSIBLE THAT COULD SHIFT NORTH A BIT.  WITH
THE IDEA THAT MOISTURE WILL STAY SOUTH...AFTERNOON TEMPERATURES WILL
JUMP TO 6-10 DEG WARMER THAN NORMAL AGAIN WITH MOSTLY SUNNY SKIES
SATURDAY AND SUNDAY.

BEYOND THAT...THE LONG RANGE GUIDANCE DECAYS THE REX BLOCK WHICH
ALLOWS THE SOUTHERN LOW TO OPEN UP AND HEAD NORTH WHICH WOULD SPREAD
THE MOISTURE UP ACROSS THE AREA.  FOR NOW I HAVE INTRODUCED CHANCE
POPS TO THE FORECAST AREA MONDAY NIGHT AND TUESDAY WITH PLENTY OF
CLOUD COVER ALTHOUGH THIS COULD SHIFT A BIT IN TIME DEPENDING ON THE
EVOLUTION OF THE BREAKDOWN OF THE BLOCK.  SOUTHERLY FLOW WILL
MAINTAIN MILD TEMPERATURES MONDAY THROUGH WEDNESDAY.  CERNIGLIA

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

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