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Climate Prediction Center

U.S. Hazards Outlook - Made Aug 29, 2016

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Day 3-7 Outlook Day 8-14 Outlook Day 8-14 Probabilistic Temperature Hazards

Valid Thursday, September 01, 2016 to Monday, September 12, 2016

Summary of Forecasts and Hazards

US Hazards Outlook
NWS Climate Prediction Center College Park MD
300 PM EDT August 29 2016

Synopsis: At the beginning of the week-1 forecast period, mid-level high pressure is expected across the Northern Plains with mid-level low pressure across the Northeast and just off the Pacific Northwest. Impacts from Tropical Depression 9 are the highlight of the week-1 hazards outlook. A surface low-pressure system is forecast to push south from Canada into the Northern Plains late in week-1. During week-2 general mid-level low pressure is anticipated across the west with mid-level high pressure forecast for the east. Another potential tropical disturbance may threaten the southeastern U.S. during the middle of week-2. Southern Alaska is expected to be impacted by a series of surface low pressure systems during the outlook period with mid-level low pressure forecast to build during week-2. Hawaii faces potential tropical cyclone impacts from Hurricanes Madeline at the outset of week-1, and Lester later in week-1.

Hazards
  • High winds across portions of the Southeast, Thu-Fri, Sep 1-Sep 2.
  • Heavy rain across portions of the Southeast and the Mid-Atlantic, Thu-Fri, Sep 1-Sep 2.
  • Flooding possible across portions of Florida.
  • Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains, Sat-Sun, Sep 3-Sep 4.
  • Heavy rain across portions of the Middle Mississippi Valley, the Great Lakes, and the Upper Mississippi Valley, Mon, Sep 5.
  • Much above-normal temperatures across portions of the Northern Plains and the Northern Rockies, Thu-Fri, Sep 1-Sep 2.
  • Flooding occurring or imminent across portions of the Middle Mississippi Valley and the Lower Mississippi Valley.
  • Slight risk of much above-normal temperatures for portions of the Great Lakes, the Mid-Atlantic, the Northeast, and the Central Appalachians, Tue-Wed, Sep 6-Sep 7.
  • Slight risk of much below-normal temperatures for portions of the Northern Intermountain Region and Northern Rockies, Thu-Sat, Sep 8-10.
  • Severe Drought across the Central Plains, the Mid-Atlantic, the Lower Mississippi Valley, the Central Great Basin, the Northern Plains, the Tennessee Valley, the Great Lakes, the Southern Appalachians, Hawaii, the Northern Rockies, the Northeast, California, the Northern Great Basin, the Southeast, the Central Appalachians, the Southern Plains, and the Southwest.
Detailed Summary

For Thursday September 01 - Monday September 05: During the course of week-1, anomalous 500-hPa ridging is favored to shift from the Northern Plains to the Northeast. Anomalous 500-hPa troughing is forecast to build into the West over the course of week-1 with this amplified pattern remaining through week-2. A cold front ahead of this trough is forecast to push eastward across the northern tier during the week. Tropical Depression 8 is expected to be off the eastern seaboard at the beginning of the forecast period, with Tropical Depression 9 potentially coming ashore on the west coast of Florida early in week-1.

Heavy rainfall (greater than 1" in 24 hours) and high winds (exceeding 30 knots) are forecast across portions of the Southeast Thu-Fri, September 1 and 2 as Tropical Depression 9 is forecast to pass from the Gulf of Mexico across Florida into the Atlantic. Dynamical model guidance currently supports this system being a tropical storm both at the time of its landfall and upon re-emerging into the Atlantic. ECMWF guidance is slightly more progressive and further east with the forecast rainfall for this system relative to the GEFS. Flooding is possible for portions of the west coast of Florida with this system, while isolated inland flooding and severe weather are possible in addition to the specified hazards on today's map. For up to date guidance on this system please visit the National Hurricane Center (NHC) at http://www.nhc.noaa.gov.

Much above-normal temperatures are forecast for portions of the Northern Rockies and Northern Plains Thursday, September 1 and Friday, September 2 where forecast high temperature anomalies could exceed 12-16 degrees F. Elsewhere, marginally elevated fire weather conditions are not shown on the forecast map, but are expected across portions of eastern Idaho and southwestern Montana on Thursday, September 1 due to the presence of low humidity, warm temperatures, breezy conditions, and the presence of dry fuels.

Aforementioned warm conditions across the Northern Rockies and Northern Plains are expected to wane with the passing of a cold front. This same boundary is forecast to bring an eastward shifting heavy rain threat to portions of the Northern and Central Plains and Upper and Middle Mississippi Valley for Saturday-Monday, September 3-5.

Hawaii is expected to see potential impacts from a pair of tropical cyclones during the week-1 period. Hurricane Madeline is forecast to pass south of the islands during September 1-2, and expected to be accompanied by heavy rains and high winds that predominantly influence the Big Island. Later in week-1 Hurricane Lester is forecast to pass North of Hawaii on September 3-4 and could bring a second round of high winds and rain. For more information on these storms please refer to the NHC or Central Pacific Hurricane Center at http://www.prh.noaa.gov/cphc/

A disturbance is expected for the Aleutians early in week-1 that is forecast to push towards Southwestern mainland Alaska during the week. Heavy rainfall is possible for the southern coastline of the state, however discrepancies between GFS and ECMWF ensemble guidance preclude a specific geographic hazard depiction at this time.

For Tuesday September 06 - Monday September 12: During week-2 an amplified pattern across the northern U.S. is forecast with anomalous 500-hPa ridging in the east and troughing for the west. Temperature-related hazards are anticipated with this pattern, with a slight risk of much above-normal temperatures for parts of the Northeast on September 6-7 and a slight risk of much below-normal temperatures for portions of the Northern Intermountain Region and Northern Rockies September 8-10. Both the GEFS and ECMWF ensemble guidance generally favor this solution, with the biggest difference being ECMWF guidance extending positive 500-hPa height anomalies further south. Both aforementioned warm and cold hazards are supported by the GEFS probabilistic extremes guidance for the 85th and 15th percentiles of daily maximum and minimum temperatures respectively.

Also of concern during week-2 is the potential for tropical cyclone related impacts to the southeastern U.S. around September 8-10 tied to a tropical wave currently exiting the African coast. As of 2 PM EDT this system is currently given a 50% chance of undergoing tropical cyclogenesis in the next 5 days by NHC. The GEFS has been reasonably consistent the last two days with forecasting this system to be in the vicinity of the southeastern coast during the second half of week-2. The 00 UTC operational ECMWF features the system, but has an interesting solution that depicts another tropical cyclone forming out of a weakening frontal zone off South Carolina around the 7th or 8th of September. Consideration was given to a heavy rainfall hazard during the middle to end of week-2 across the Southeast, but it was left off the map due to: lack of model consensus, the substantial forecast lead time, and the initial disturbance not even entering the Atlantic as of yet. The forecast evolution of this system will continue to be monitored closely over the course of the week for any potentially hazardous impacts to U.S. interests.

According to the U.S. Drought Monitor issued on August 25, the coverage of severe or greater drought decreased slightly to 7.41 percent from 7.71 percent. Improvements were realized across central Texas and the Tennessee Valley.

Forecaster: Daniel Harnos

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Click here to see a display of the GFS Ensemble Forecasts

Please consult local NWS Forecast Offices for short range forecasts and region-specific information.


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