Wednesday, July 20, 2011

July 20 Evening Briefing

Storms did NOT develop, just as the models had predicted.

Unfortunately, at this late hour, I'm not going to provide an extended discussion

Mesoscale Discussion #1671

Mesoscale Discussion #1671 has been issued for NE Minnesota and North Wisconsin.

Discussion... Convective initiation expected within the next hour in NE Minnesota within an area of strong SBCAPE and an eroded CINH. Storms are expected to develop very soon now that the cap has been eroded from the region. EHI/STP parameters not too impressive in NE Minnesota, but elevated in Wisconsin. Derecho Composite is interesting, though, as it appears to have more lust than other parameters in the MN area. Damaging wind threat is there, and hail will be possible. I am anticipating this to be more of a scattered cell development rather than one large MCS (storm cluster). However, should the cells unite into a MCS, I expect the damaging wind threat to rise.
Interestingly enough, 23z RR model run is not showing any precipitation to come from the area. 22z HRRR also not for precipitation, but do believe precipitation may arise. I still have my doubts, but the SPC appears to have a firm opinion on this.
23z RUC develops small area of convection which quickly pushes away into Canada.
Again, I still have my doubts, but would rather say precipitation and be wrong than deny precipitation and be wrong.

1:00PM Weather Briefing- WI/MN July 20 Severe Storms

Discussion... After observing 16z RR, 15z HRRR and 16z RUC, it looks like the worst that will hit Minnesota will be some light to moderate convection. I do not anticipate major severe weather to occur, and storm coverage/development is in question.
Analysis indicates strong CINH/cap guarding the area being monitored for storm development. CINH (warm air aloft that suppresses rising air/thunderstorms) levels are around -300 to -450, considered very tough to break. While supercell composites and EHI levels are rising in NE Minnesota and North Wisconsin, the CINH is still a big factor. Current CAPE levels are at 2000-3000 j/kg near the warm front, while at 4000 j/kg farther east.
Will introduce a chance for thunderstorms, with that chance turning likely should the CINH weaken/break.
Clouds also remain in NE Minnesota, which could hamper stronger storms.

Forecast Discussion- Minnesota/Wisconsin (July 20)( 11 AM CDT)

EHI: Spinning and energy in the atmosphere. Values above 2 considered elevated.

STP: Values above 1 considered elevated

SCP: Values above 4 considered elevated
SCP: Supercell Composite. Shows chance for supercells.
EHI: Energy Helicity Index. See image w/ caption for description
STP: Significant tornado parameter. Values above 2 associated with F2+ tornadoes.

Discussion... Cold front in question to ignite thunderstorms in WI/MN is currently beginning its trek eastward from the Dakotas.
It looks like thunderstorms have already developed ahead of the cold front in the Dakotas, as several outflow boundaries have surfaced near the cold front itself.
Convection should begin this afternoon for MN/WI

Big issue is model runs. Have just observed 14z run of RR, which indicates no convection should occur in MN. Showers and an isolated storm instead. Observing the 13z HRRR ignited an MCS (storm cluster) in MN and tracked sharply NE, missing Wisconsin. HRRR indicates MCS in MN may become tornadic, as close detail indicates a more hook-like cell in the MCS.
14z RUC appears to attempt and initiate convection in East Central Minnesota, but appears to die out. A small bowing structure forms at about 5 pm in far NE Minnesota and that evolves into a smaller MCS as it moves into Canada.

In summary...whole idea of severe storms this afternoon is clouded by the models. Indicators posted above in images appear to favor Wisconsin, so this may be a case of wrong place, right time for WI/MN.
Will post later updates as this confusion will warrant another look.

StormTrack: July 20: Tornadic Storm in Roseau, MN

The Weather Centre team has identified an area of likely rotation and a possible tornado occurring in Roseau, Minnesota.

Discussion... RUC has evolved storm nicely in the 12z run. RUC projects cell to move over US/Canada border and out of NWS responsibility area in the next couple hours.
Analysis indicates STP and SCP parameters aren't impressive in the cell in question, but EHI and CAPES are sufficient for tornadic thunderstorms.
This couplet of winds as seen above is interesting, and we will continue to watch it as it moves towards the Canadian border.

Current Heat Index

Tomorrow's High Temperatures

High Temperatures Today

July 20: Weakening Tropical Storm Bret Briefing

Bret is a tropical storm with maximum sustained winds of 50 MPH. Central Pressure is 1001 millibars. Bret is moving NE at 7 MPH.

Because Bret is so weak, we will not feature ensembles or wind probabilities.

We do anticipate Bret to continue weakening throughout the day today and tomorrow.

July 20- Morning Low in Atlantic Briefing


1. SATELLITE IMAGES THIS MORNING INDICATE THAT SHOWER ACTIVITY
ASSOCIATED WITH A LOW PRESSURE AREA ABOUT 440 MILES EAST OF BERMUDA
HAS BECOME BETTER ORGANIZED.  ADDITIONAL DEVELOPMENT OF THIS SYSTEM
IS POSSIBLE DURING THE NEXT DAY OR SO BEFORE IT REACHES COOLER
WATERS.  THIS SYSTEM HAS A HIGH CHANCE...60 PERCENT...OF BECOMING A
SUBTROPICAL OR TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT
MOVES NORTHEASTWARD AT AROUND 20 MPH. 

July 20- Morning Hurricane Dora Update (Cat. 1)

Dora is currently a Category 1 hurricane with maximum sustained winds of 90 MPH. Central Pressure 981 millibars. Dora is moving west-northwest at 18 MPH.
Satellite images indicate Dora is trying to develop an eye in her core. It is expected that, as Dora gathers strength, that will become an easy task for her to accomplish.
Dora is a fairly big hurricane, with rain bands impacting Mexico's Coast.
Maximum wind speed probabilities indicate Dora may not have as much chance to turn into a major hurricane as originally thought. While still elevated, the maximum chance for Dora to reach Category 3 strength or higher is at 44%.

Ensembles for tracks and intensity forecasts are all fairly organized this morning. The consensus is to keep Dora away from land while still gathering strength. Looking at intensity forecasts, you can see why i'm casting doubt on Dora reaching major hurricane strength. Only/At Least 3 ensemble members place Dora at a weak to moderate Category 3 hurricane before dropping off and dissipating 6 days out.

July 19 Evening Bow Echo Analysis

Unfortunately, it looks like the bow echo did stay strong and moved more west than we had anticipated.
We did believe at least a bit of the bow echo would shift more westerly as the 2z RUC/HRRR model runs came in last night, but no one predicted the storms to stay together while moving SSE.
Although the storms did weaken as they moved into a CINH area with warm air aloft that prevents rising air from doing just that, it was a lesser area of CINH than I believe other people had seen coming. I had debated on whether the CINH was enough to prevent the strong storms, and eventually decided yes, so that was my forecasting error.
You can access a loop of the radar from last night by following the link below.
http://www.spc.noaa.gov/sfctest/new/archiveviewer.php?sector=20&parm=rgnlrad