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National Situation Update: Monday, September 21, 2009

Homeland Security Threat Level: YELLOW (ELEVATED).

National Weather

Midwest
There is a possibility of rain across much of the region today.   Some heavy showers and a few thunderstorms are predicted for the Eastern areas. A few areas in Michigan, Indiana and Ohio could have over several inches of rain overnight.  A cold front spreads showers and thunderstorms across the Plains and into the Mississippi Valley.  A few of the thunderstorms in the Missouri Valley could contain large hail and damaging wind gusts this afternoon and evening.   High temperatures in the 70s to lower 80s from the Mississippi Valley eastward, and temperatures in the 50s and 60s over the Plains.
South
A new upper level low forms today and Tuesday over the Rockies and Plains and will remain nearly stationary throughout the remainder of the week.  The low should continue to draw moisture off the Gulf of Mexico causing scattered showers and thunderstorms over the South through the week.   A continuing flood threat continues due to locally heavy rain.
West
A stalled upper level low over the central/southern Rockies and Plains brings cool fall weather with lowering snow levels, while a strong ridge aloft brings heat to the West Coast, Northwest and into the northern Rockies.  Today the upper low brings rain, showers and a few thunderstorms from portions of Montana to New Mexico. It also brings gusty winds of 25 to 40 mph in the higher terrain of Wyoming, Colorado and New Mexico.  Sporadic shower activity moves over Montana, Idaho, Utah, and New Mexico.  Freeze watches for parts of the Intermountain West tonight and Tuesday morning.  Hot temperatures continue from the deserts to the Northwest with highs in the 70s and 80s to the 90s and lower 100s in the deserts.  A heat advisory is in effect for the San Francisco Bay area.
Northeast
Lows overnight will cause temperatures to drop in the 40s for the north and in the 50s to 60s for the south. A few of the normally colder valleys in northern New York and New England could dip back into the middle 30s tonight.  Moisture moves into the region from the South during the beginning of the week.  Clouds and a few showers are possible from western New York south to western Virginia today and moving into the remainder of the region by Tuesday. (NOAA's National Weather Service, Various Media Sources)

Fire Weather

A strong high pressure system will build over the western U.S. early next week bringing an extended period of hot weather that will last through Friday. Temperatures next week will be 10 to 20 degrees above average with record highs possible in some areas.

High pressure will strengthen over the eastern Pacific this weekend and move inland over Oregon and Northern California remaining nearly stationary through Wednesday. Dry northeast winds around the high will increase the offshore flow and bring hot dry weather to Southern California.

The system will build into Northern California on Monday with afternoon high temperatures on Monday and Tuesday ranging from the mid to upper 90s around San Francisco Bay and the northern part of Monterey Bay. Inland afternoon temperatures will reach the upper 90s and to near 105. Offshore winds will continue at least through Tuesday along with hot afternoons. Though this will not be a strong offshore wind event in the Bay area, the very dry fuels, hot temperatures, and offshore winds of 10 to 20 mph will bring a critical fire weather period to the North Bay mountains through Tuesday.

Farther south, offshore flow near the surface is expected to increase late Monday night into Tuesday bringing the potential for moderate offshore winds to the passes and canyons of Los Angeles and Ventura counties weakening somewhat Tuesday night into Wednesday. The offshore winds are expected to bring significant warming and drying on Tuesday and Wednesday with the potential for widespread and long duration single digit humidities as well as widespread triple digit heat. High temperatures at the beaches will mostly be in the 80s. But just a few miles from the coast the highs will be in the 90s to near 100. Inland valley and foothill temperatures will range from 95 to 110.

The hot, dry conditions and weak offshore flow will elevate the fire danger next week. While the offshore winds are not expected to be very strong, the combination of triple digit heat, single digit humidities, and very dry fuels will elevate the fire hazard potential next week

California Wildfire

Station Fire
Located in the Angeles National Forest, investigation reveals that arson caused the fire. Fire crews continue to mop up, patrol areas, and continue fire suppression repair. 160,557 acres burned; 93% contained. Estimated containment date has been moved forward to Tuesday, September 22, 2009. FMAG-2830-FM-CA approved August 28, 2009.
Vail Fire
Fire located in Riverside County, CA has burned 340 acres and is 100% contained. 15 residential structures have been destroyed. All evacuations have been lifted. (Region IX, NIFC)

Tropical Weather Outlook

Atlantic
Tropical cyclone formation is not expected during the next 48 hours.

Eastern Pacific
Area 1
A small area of low pressure located about 700 miles south of the southern tip of Baja California is moving west-northwestward at around 10 to 15 mph.  Conditions appear favorable for gradual development of this system over the next couple of days. There is a low chance (less than 30%) of this system becoming a tropical cyclone during the next 48 hours.

Central
No tropical cyclones are expected through this afternoon.

Western Pacific
No tropical cyclones are expected through this afternoon. (NOAA, HPC, National Hurricane Center, NWS Tiyan, GU, Central Pacific Hurricane Center and the Joint Typhoon Warning Center, Region IX)

Earthquake Activity

A 6.3 magnitude earthquake occurred approximately 80 miles NNW of, Gauhati, Assam, India at 4:53 a.m. EDT. The quake was recorded at a depth of 4.5 miles. No reports of any injuries or damages.  (USGS, Earthquake Hazards Program)

Preliminary Damage Assessments

No new activity (FEMA HQ)

Wildfire Update

National Preparedness Level:  2
National Fire Activity as of Sunday, September 20, 2009:
Initial attack activity:  Light (82 new fires)
New large fires:  2
Large fires contained:  0
Uncontained large fires:  6
States affected:  AZ, CA, ID, OR and WA. (NIFC)

Disaster Declaration Activity

No new activity (FEMA HQ)

Last Modified: Monday, 21-Sep-2009 08:00:02 EDT