Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 060434
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
934 PM MST SUN JUL 5 2015

.SYNOPSIS...A PACIFIC LOW PRESSURE SYSTEM OFF THE CALIFORNIA COAST
WILL BRING DRIER AIR IN FROM THE WEST THE NEXT COUPLE OF DAYS. THIS
WILL RESULT IN A GENERAL DECREASE IN THUNDERSTORM ACTIVITY. DAYTIME
TEMPERATURES WILL REMAIN CLOSE TO SEASONAL NORMALS.

&&

.DISCUSSION...THE UPPER WEATHER PATTERN IS DEFINED BY AN UPPER LOW
POSITIONED OFF THE CALIFORNIA COAST AND A POSITIVELY TILTED RIDGE OF
HIGH PRESSURE ALOFT EXTENDING FROM CHIHUAHUA MEXICO INTO WESTERN
TEXAS. TODAY WAS A RATHER ACTIVE DAY ACROSS THE WESTERN HALF OF THE
FORECAST AREA AS PORTIONS OF THE TOHONO OODHAM NATION RECEIVED
BETWEEN 2 AND 3 INCHES OF RAIN...LOCALLY MORE. CENTRAL PIMA COUNTY
WAS THE BATTLEGROUND BETWEEN THE DRY AIR MOVING INTO SW ARIZONA FROM
THE SW-W AND THE MOIST AIRMASS ENTRENCHED ACROSS THE AREA. THE 00Z
KTWC SOUNDING INDICATED A PWATER VALUE OF 1.81 INCHES...WHICH WAS A
06/00Z RECORD FOR PWATER FOR THE DATE. A DISTURBANCE EMBEDDED IN THE
FLOW ALONG THIS MOISTURE BOUNDARY MOVED INTO W/CENTRAL PIMA COUNTY
EARLY THIS AFTERNOON...AND WITH THE MOIST AIRMASS IN PLACE...WAS
ABLE TO PRODUCE THE SIGNIFICANT RAINFALL.

HOWEVER...STORMS STRUGGLED AS THEY TRACKED EAST OF TUCSON. THEY
STILL PRODUCED LOCALIZED HEAVY RAIN...BUT THE COMBINATION OF THE
CLOUD COVER THAT KEPT TEMPERATURES COOLER AND THE DRIER AIR ALOFT
KEPT DEEP CONVECTION AT BAY. IN ANY EVENT...STORMS THIS EVENING HAVE
MOSTLY DIED OFF. I AM STILL KEEPING IN A SLIGHT CHANCE OF SHOWERS
OVERNIGHT AS ANY VERY WEAK DISTURBANCE IN THE SOUTHWESTERLY FLOW MAY
TRIGGER A VERY LIGHT SHOWER. OTHERWISE...IT SHOULD BE A QUIET NIGHT.

&&

.PREV DISCUSSION...WATER VAPOR IMAGERY AND 05/12Z UPPER-AIR PLOTS
SHOW A RIDGE CENTERED OVER EASTERN NEW MEXICO. MEANWHILE...A PACIFIC
LOW PRESSURE SYSTEM IS SPINNING WELL WEST OF THE SOUTHERN CALIFORNIA
COAST. A SWATH OF DRY MID TO UPPER LEVEL AIR CAN BE SEEN OVER THE
EASTERN PACIFIC WATERS...THE BAJA PENINSULA...NORTHWESTERN SONORA
AND ACROSS PARTS OF SOUTHERN CALIFORNIA AND INTO WESTERN ARIZONA.
MEANWHILE...VISIBLE AND IR SATELLITE IMAGERY AND RADAR MOSAIC FROM
AROUND THE REGION SHOW ANOTHER MCV THAT HAS DEVELOPED AS A RESULT OF
LAST NIGHTS CONVECTION...WITH THE CENTER OF THIS FEATURE JUST WEST
OF DOUGLAS IN COCHISE COUNTY.

WATER VAPOR IMAGERY SHOWS A SHARP DEMARCATION BETWEEN DRY AIR TO OUR
WEST AND MOIST AIR TO THE EAST. IN ADDITION...THIS MORNINGS KTWC
SOUNDING REVEALED A PW OF 1.71 INCHES. THE MOST RECENT SATELLITE
DERIVED BLENDED TOTAL PRECIPITABLE WATER IMAGERY SHOWS VALUES OF 1.4
INCHES OVER SOUTHWESTERN ARIZONA AND 1.8 OVER THE CENTRAL PART OF MY
FORECAST AREA...WITH VALUES APPROACHING 2 INCHES OVER THE NORTHERN
GULF OF CALIFORNIA. THE THUNDERSTORM ACTIVITY FIRED ALONG THIS
DEMARCATION EARLIER TODAY AND THE MOST RECENT RADAR MOSAIC SHOW
SCATTERED TO NUMEROUS ACTIVITY...MAINLY WEST OF INTERSTATES 10 AND
19 AND SOUTH OF INTERSTATE 8. RADAR RAINFALL ESTIMATES WITH THESE
STORMS HAVE BEEN QUITE HEALTHY AND WITH THE HIGH PW VALUE OF THIS
MORNINGS SOUNDING...NOT TO MENTION THE LATEST SATELLITE DERIVED
ESTIMATES...IT LOOKS LIKE HEAVY RAIN AND THE RESULTANT STREAM
FLOODING/FLOODING OF LOW LYING AREAS WILL BE THE ISSUE FOR THE DAY.
THE NORTHERN AND EASTERN PARTS OF THE TOHONO O`ODHAM NATION IS
CURRENTLY TAKING THE BRUNT OF THIS HEAVY RAIN. A SMALL STREAM FLOOD
ADVISORY HAS BEEN ISSUED TO INCLUDE CENTRAL AND WESTERN PORTIONS OF
PIMA COUNTY AS WELL AS SOUTHERN PORTIONS OF PINAL COUNTY UNTIL 345
PM MST. THE 12Z RUN OF THE U OF A WRF/NAM SEEMS TO HAVE CAPTURED THE
ONGOING RADAR SCENARIO QUITE WELL.

AFTER TODAY...WE SHOULD SEE A DECREASE IN THUNDERSTORM ACTIVITY AS
THE UPPER LOW OVER THE PACIFIC MAKES ITS WAY TOWARD THE WEST COAST
AND EVENTUALLY INTO THE GREAT BASIN BY LATE IN THE WORK WEEK. THIS
WILL RESULT IN SOUTHWESTERLY WINDS THAT WILL PUSH MOISTURE TO THE
EAST.

&&

.AVIATION...VALID THRU 07/06Z.
MOSTLY CLOUDY SKIES WITH A SLIGHT CHANCE OF -SHRA WILL BE POSSIBLE
OVERNIGHT...ESPECIALLY IN THE EAST ALONG THE ARIZONA/NEW MEXICO
BORDER. DRIER AIR MOVING IN FROM THE WEST WILL GENERALLY DECREASE
STORM COVERAGE TOMORROW. HOWEVER....SCATTERED COVERAGE OF
-TSRA/-SHRA IS IN STORE MONDAY...WITH THE BULK OF THIS PRECIPITATION
TO BE FROM KTUS EASTWARD/SOUTHWARD TO THE NEW MEXICO/INTERNATIONAL
BORDERS. OTHERWISE...CLOUD DECKS WILL MAINLY BE AT OR ABOVE 8K FT
AGL AND SURFACE WIND WILL GENERALLY BE LESS THAN 10 KTS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...SCATTERED SHOWERS AND THUNDERSTORMS WILL RETURN
MAINLY FROM TUCSON EASTWARD AND SOUTHWARD MONDAY AFTERNOON.
THEREAFTER...SOMEWHAT REDUCED COVERAGE OF SHOWERS AND THUNDERSTORMS
SHOULD PREVAIL STARTING TUESDAY AND CONTINUING INTO NEXT WEEKEND.
OTHERWISE...GENERALLY LIGHT TERRAIN DRIVEN WINDS WILL PREVAIL
OUTSIDE OF THUNDERSTORM INFLUENCES.

&&

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

&&

$$


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