USA Weather — Severe Weather Division
This outlook is expired and is no longer valid.
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE INTERIOR PACIFIC NORTHWEST...
...SUMMARY...
SEVERE THUNDERSTORMS PRODUCING DAMAGING WINDS OF 60-75+ MPH, LARGE HAIL, AND PERHAPS A TORNADO OR TWO ARE EXPECTED ACROSS THE PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES THIS AFTERNOON INTO THIS EVENING.
...PACIFIC NORTHWEST INTO NORTHERN ROCKIES...
MORNING WATER VAPOR IMAGERY INDICATES A LARGE UPPER LOW STALLED ACROSS THE CENTRAL WEST COAST REGION, WITH MULTIPLE SUBTLE IMPULSES/VORTICITY LOBES ON THE SOUTHERN AND EASTERN SIDE OF THE LOW SPREADING COUNTER-CLOCKWISE WITHIN A BELT OF STRONG MID TO UPPER LEVEL FLOW. THE MOST NOTABLE OF THESE IS A WELL-DEFINED SECONDARY VORTICITY LOBE ON THE SOUTHEAST SIDE, WHICH IS FORECAST TO SPREAD NORTH AND NORTHWEST THIS AFTERNOON AND EVENING ACROSS THE INTERIOR PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES. AHEAD OF THIS IMPULSE, SUFFICIENT DIURNAL HEATING WITHIN AN ANOMALOUSLY MOIST SURFACE AIRMASS (DEWPOINTS IN THE UPPER 50S TO LOW 60S) UNDERNEATH VERY STEEP LOW AND MID-LEVEL LAPSE RATES WILL RESULT IN NEAR RECORD HIGH MLCAPE VALUES IN THE 1000-1500 J/KG RANGE ACROSS EASTERN OREGON AND WASHINGTON SPREADING INTO MUCH OF NORTHERN AND WESTERN IDAHO INTO MONTANA. SOME GUIDANCE SUGGESTS POTENTIAL FOR LOCALLY HIGHER VALUES AROUND 2000 J/KG DURING PEAK HEATING THIS AFTERNOON.
BY EARLY AFTERNOON, SCATTERED THUNDERSTORM INITIATION IS EXPECTED TO OCCUR ACROSS FAR NORTHERN CALIFORNIA/NEVADA INTO SOUTHEAST OREGON AS THE VORTICITY LOBE BEGINS TO MOVE OVERHEAD. FAIRLY STRONG DEEP-LAYER SHEAR OF 40-60KT, WITH LENGTHY HODOGRAPHS, ALONG WITH MODERATE TO STRONG INSTABILITY, WILL SUPPORT RATHER QUICK ORGANIZATION INTO MULTIPLE NORTHWARD TO NORTHWESTWARD-PROPAGATING MULTICELL CLUSTERS AND LINE SEGMENTS, PERHAPS ALONG WITH AN EMBEDDED SUPERCELL OR TWO. VERY STEEP LOW-LEVEL LAPSE RATES AIDED BY STRONG MIXING WILL SUPPORT INCREASING POTENTIAL FOR DAMAGING WIND GUSTS OF 60-75+ MPH WITH INTENSE OUTFLOW/DOWNBURSTS. LARGE TO VERY LARGE HAIL IS ALSO A CONCERN WITHIN STRONGER UPDRAFTS AND ESPECIALLY WITHIN HIGHER TERRAIN. A TORNADO OR TWO MAY ALSO BE A CONCERN, ESPECIALLY GIVEN AN INCREASING SIGNAL FOR LOW-LEVEL HELICITY IN THE 150-200 M2/S2 RANGE THIS AFTERNOON. FAIRLY NUMEROUS COVERAGE HAS CONTINUED TO BE INDICATED IN VARIOUS CAMS. GIVEN THE AFOREMENTIONED ENVIRONMENT, ENOUGH CONFIDENCE IN SCATTERED TO NUMEROUS DAMAGING WIND GUSTS TO OUTLINE A BROAD ENHANCED RISK FOR SEVERE STORMS. CONTINUED NORTHWARD TO NORTHWESTWARD PROGRESSION IS EXPECTED THROUGHOUT THE AFTERNOON AND EVENING, WITH DAMAGING WINDS AND LARGE HAIL LIKELY TO REMAIN A THREAT.
...CENTRAL GULF COAST...
A SHORTWAVE IMPULSE ACROSS THE CENTRAL GULF INTO THE LOWER MISSISSIPPI VALLEY WILL CONTINUE TO SLOWLY SPREAD NORTHWARD TODAY. RADAR IMAGERY INDICATES A LARGE CLUSTER OF STORMS DEVELOPING ACROSS EASTERN LOUISIANA INTO SOUTHERN MISSISSIPPI HEAD OF THIS IMPULSE THIS MORNING. A VERY MOIST AIRMASS AND SUFFICIENT HEATING WILL SUPPORT STRONG DESTABILIZATION TODAY. WHILE DEEP-LAYER SHEAR WILL REMAIN FAIRLY WEAK, LIKELY 20-25KT AT BEST, AN INCREASING SIGNAL FOR NUMEROUS STORM COVERAGE AS THIS CLUSTER CONTINUES TO INTENSIFY AND SPREAD NORTHEAST IS APPARENT. ISOLATED INSTANCES OF STRONG TO MARGINALLY SEVERE WATER-LOADED DOWNBURSTS, ESPECIALLY WHERE STORM-SCALE INTERACTIONS AND MERGERS OCCUR.
...CENTRAL KANSAS...
AN MCV CONTINUES TO MIGRATE NORTHWESTWARD ACROSS THE CENTRAL PLAINS TODAY, CURRENTLY LOCATED ACROSS NORTHEASTERN OKLAHOMA INTO SOUTHERN KANSAS. DESPITE WIDESPREAD CLOUD COVER, ENOUGH LOW-LEVEL MOISTURE WITHIN MODESTLY STEEP LAPSE RATES SHOULD SUPPORT WEAK TO MODEST INSTABILITY, POTENTIALLY INCLUDING 3CAPE OF 100-150 J/KG BY THIS AFTERNOON. FAVORABLY CURVED HODOGRAPHS SUPPORTING STRENGTHENING HELICITY ON THE NORTHERN AND EASTERN SIDE OF THE LOW. WITH SCATTERED TO NUMEROUS SHOWERS AND STORMS TODAY, A FEW LOW-TOPPED TRANSIENT SUPERCELLS COULD EVOLVE IN THIS ENVIRONMENT, POTENTIALLY ASSOCIATED WITH A BRIEF TORNADO OR TWO.
...ROCKIES FRONT RANGE...
ISOLATED TO WIDELY SCATTERED CONVECTIVE DEVELOPMENT IS EXPECTED THIS AFTERNOON AND EVENING ON THE ROCKIES FRONT RANGE FROM NORTHERN NEW MEXICO INTO SOUTHERN WYOMING. A SUFFICIENTLY UNSTABLE AIRMASS ALONG WITH STRONG SHEAR AND COOL MID-LEVEL TEMPERATURES WILL SUPPORT THE THREAT FOR ISOLATED LARGE HAIL WITHIN MORE INTENSE UPDRAFTS, PARTICULARLY THOSE OVER HIGHER ELEVATIONS OR THAT HAVE TOPOGRAPHIC ENHANCEMENT.