September 2021 - hpo-ims - Udfcd-Lists.Org

by f2p2＠udfcd.org

Time: 919 AM Fri September 3, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- SEASONAL TEMPERATURES WITH A ROUND OR TWO OF THUNDERSTORMS THIS AFTERNOON/EVENING - Temperatures will be at or slightly below seasonal averages today over the District with highs reaching the upper 70's to lower 80's over the plains. Normal high for Denver today is 84 degrees. An upper level disturbance is on the approach and may result in an isolated rain shower this morning, favoring the higher terrain. - As the upper level disturbance moves through the District this afternoon it is expected to generate a round or two of thunderstorms between 1-7pm. Upper level steering winds from SW to NE at 15-20mph will keep storms moving along at a brisk pace but stronger storms will be capable of producing brief heavy rainfall that may lead to excessive runoff roadways and smaller creeks/streams. Favored areas for stronger storms at this time looks to be E of I-25 and S of I-70. In addition to brief heavy rainfall strong thunderstorms may also contain gusty winds and large hail. - After 7pm the main round or two of storms is expected to have pushed eastward with lingering more isolated light rain showers remaining possible until around 10pm. Beyond 10pm dry conditions are expected for the remainder of the evening/overnight period. STORM RAINFALL POTENTIAL AND DURATION: Weak thunderstorms will produce 0.1-0.4" of rainfall in 10-30 minutes. Moderate to strong thunderstorms will have the potential to produce heavy rainfall of 0.4-1.2" in 10-30 minutes. WORST CASE SCENARIO: Training of strong thunderstorm cells or a slower moving large thunderstorm may result in up to 2.4" of rainfall in 60-90 minutes. A LOOK AHEAD: Behind the disturbance that moves through later today temperatures will be similar on Saturday in the 70's and lower 80's for highs over the plains. A more stable atmosphere will be in place over the plains with possibly an isolated late afternoon thunderstorm, otherwise thunderstorm activity will favor the foothills and Palmer Divide on Saturday. Sunday and Monday are trending dry with warming temperatures. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains Â Â Â Adams 100 PM TO 700 PM 0.1" (80%) to 0.4" (60%) to 1.2" (20%) HIGH Arapahoe 100 PM TO 700 PM 0.1" (80%) to 0.4" (60%) to 1.2" (20%) HIGH Broomfield 100 PM TO 700 PM 0.1" (80%) to 0.4" (60%) to 1.2" (20%) HIGH Denver 100 PM TO 700 PM 0.1" (80%) to 0.4" (60%) to 1.2" (20%) HIGH Boulder 1200 PM TO 700 PM 0.1" (80%) to 0.4" (50%) to 1.2" (15%) MOD Douglas 1200 PM TO 700 PM 0.1" (80%) to 0.4" (60%) to 1.2" (20%) HIGH Jefferson 1200 PM TO 700 PM 0.1" (80%) to 0.4" (50%) to 1.2" (15%) MOD Foothills above 6500ft Â Â Â Boulder 1100 AM TO 600 PM 0.1" (90%) to 0.4" (50%) to 1.2" (10%) LOW Douglas 1100 AM TO 600 PM 0.1" (90%) to 0.4" (50%) to 1.2" (10%) LOW Jefferson 1100 AM TO 600 PM 0.1" (90%) to 0.4" (50%) to 1.2" (10%) LOW MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789 Â Â Â F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]

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Flash Flood Prediction Program

by f2p2＠udfcd.org

Time: 854 AM Thu September 2, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- WIDELY SCATTERED AFTERNOON/EVENING SHOWERS/THUNDERSTORMS FAVORING THE HIGHER TERRAIN - Behind the trough of low pressure that moved through overnight temperatures will be cooler today with highs in the 70's to lower 80's over the plains. With more moisture to work with at the surface today isolated to widely scattered showers and thunderstorms will develop as early as noon over the foothills. - Rain showers and weak to moderate thunderstorms are expected to favor the higher terrain of the foothills and areas S of I-70 this afternoon over the Palmer Divide. Best chances for shower and thunderstorm activity will be between 1-9pm with lingering showers and possibly a weak thunderstorm possible until around midnight. - Showers and thunderstorms will be relatively fast moving from W to E at around 20mph helping to reduce point rainfall amounts from a single storm. Typical storms are expected to be weak to moderate in intensity but a stronger storm cannot be completely ruled out. If a stronger storm were to develop it would be capable of producing brief heavy rainfall, likely favoring the foothills and Palmer Divide region outside the District. STORM RAINFALL POTENTIAL AND DURATION: Rain showers will produce a trace to 0.1" of rain. Weak to moderate thunderstorms will produce 0.1-0.4" in 10-30 minutes. WORST CASE SCENARIO: A strong, slower moving thunderstorm is able to develop with the potential to produce heavy rainfall of up to 0.4-1.2" in 10-30 minutes. A LOOK AHEAD: Temperatures will continue to trend in the 70's and 80's for highs on Friday. Friday afternoon an upper level disturbance will move through and likely produce a round or two or moderate to strong thunderstorms sometime between noon-6pm. The thunderstorms are expected to be relatively fast moving but will be capable of producing brief heavy rainfall and possibly severe weather with hail and gusty winds being the primary threats. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains Â Â Â Adams 100 PM TO 900 PM Trace (75%) to 0.2" (40%) to 0.4" (10%) NONE Arapahoe 100 PM TO 900 PM Trace (75%) to 0.2" (40%) to 0.4" (10%) NONE Boulder 100 PM TO 900 PM Trace (80%) to 0.2" (45%) to 0.4" (15%) LOW Broomfield 100 PM TO 900 PM Trace (75%) to 0.2" (40%) to 0.4" (10%) NONE Denver 100 PM TO 900 PM Trace (75%) to 0.2" (40%) to 0.4" (10%) NONE Douglas 100 PM TO 900 PM Trace (90%) to 0.2" (50%) to 0.4" (20%) LOW Jefferson 100 PM TO 900 PM Trace (90%) to 0.2" (50%) to 0.4" (20%) LOW Foothills above 6500ft Â Â Â Boulder 1200 PM TO 900 PM Trace (95%) to 0.2" (50%) to 0.4" (25%) LOW Douglas 1200 PM TO 900 PM Trace (95%) to 0.2" (50%) to 0.4" (25%) LOW Jefferson 1200 PM TO 900 PM Trace (95%) to 0.2" (50%) to 0.4" (25%) LOW MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789 Â Â Â F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]

3 years, 3 months

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Flash Flood Prediction Program

by f2p2＠udfcd.org

Time: 929 AM Wed September 1, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- INCREASING CLOUD COVER WITH LATE AFTERNOON AND EVENING SHOWERS/THUNDERSTORMS POSSIBLE - A trough of low pressure is on the approach and will result in an increase in mid and upper level moisture leading to more cloud cover over the District today. The lower levels of the atmosphere remain relatively dry and will take some time to moisten resulting in a late onset to the chances for showers and thunderstorms. - Most of the moisture associated with the trough of low pressure will remain along and west of the Continental Divide today. Chances for showers and weak thunderstorms increase over the higher terrain between 2-4pm and over the plains between 4-6pm. Best chances for showers and perhaps a weak to moderate thunderstorm will be from 6-10pm with lingering activity possible until midnight. Beyond midnight a few lingering rain showers may persist, favoring W/NW areas of the District. - Upper level steering winds from SW to NE at 15-20mph will keep the showers and any thunderstorms that manage to develop moving along, reducing the threat for heavy rainfall despite moisture on the increase as the day wears on. Although not expected if a strong thunderstorm is able to develop this evening brief heavy rainfall would be possible. If the threat for strong thunderstorms increases the HPO will be updated. STORM RAINFALL POTENTIAL AND DURATION: Rain showers will produce a trace to 0.1" of rain. Weak to moderate thunderstorms will have the potential to produce 0.1-0.3" in 10-30 minutes. WORST CASE SCENARIO: A strong thunderstorm is able to develop this evening with the potential to produce 0.3-0.9" in 10-30 minutes. A LOOK AHEAD: Much cooler Thursday with highs only in the upper 70's to lower 80's over the plains. With more moisture to work with if temperatures warm sufficiently thunderstorms will have the potential to produce brief heavy rain. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains Â Â Â Adams 600 PM TO 1200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Arapahoe 600 PM TO 1200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Broomfield 600 PM TO 1200 AM THU Trace (70%) to 0.1" (35%) to 0.3" (15%) NONE Denver 600 PM TO 1200 AM THU Trace (70%) to 0.1" (35%) to 0.3" (15%) NONE Boulder 500 PM TO 200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Douglas 500 PM TO 200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Jefferson 500 PM TO 200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Foothills above 6500ft Â Â Â Boulder 400 PM TO 400 AM THU Trace (85%) to 0.1" (50%) to 0.3" (20%) NONE Douglas 400 PM TO 400 AM THU Trace (85%) to 0.1" (50%) to 0.3" (20%) NONE Jefferson 400 PM TO 400 AM THU Trace (85%) to 0.1" (50%) to 0.3" (20%) NONE MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789 Â Â Â F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]

3 years, 3 months

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hpo-ims September 2021