Impressive Storm

An impressive, record breaking storm system continues to impact the Upper Midwest, Great Lakes and Ohio Valley region as I type this blog.  Blizzard warnings, heavy snowfall, very strong winds (thunderstorm and non-thunderstorm), severe thunderstorms and tornadoes have impacted nearly 1/2 of the CONUS over the last 24 hours. ~ CS

Here is a look at the pressures, frontal positions and selected METARS as of late this afternoon:



Here is a Public Information Statement from the NWS in Duluth, MN:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE DULUTH MN
1055 AM CDT TUE OCT 26 2010

...MINNESOTA ALL TIME LOWEST PRESSURE RECORD BROKEN THIS MORNING...
...PRESSURE IS STILL FALLING AND WILL CONTINUE INTO THE AFTERNOON...

REMEMBER THAT THIS INFORMATION IS PRELIMINARY. THE LOW IS STILL STRENGTHENING SO THE VALUES LISTED BELOW ARE LIKELY TO CHANGE. AN UNUSUALLY INTENSE LOW WAS AFFECTING THE STATE OF MINNESOTA THIS MORNING.

AT 1013 AM CDT...THE AUTOMATED WEATHER OBSERVING SYSTEM AT AITKIN MINNESOTA RECORDED A 962.3 MILLIBAR /28.42 INCHES/ PRESSURE. THIS BREAKS THE ALL TIME MINNESOTA STATE RECORD FOR THE LOWEST OBSERVED PRESSURE.

THE PREVIOUS RECORD WAS 962.6 MB SET ON NOVEMBER 10 1998 AT ALBERT LEA AND AUSTIN IN SOUTHERN MINNESOTA. IT SHOULD ALSO BE NOTED THAT DULUTH BROKE THEIR PRESSURE RECORD. AS OF 1028 AM...THE PRESSURE AT DULUTH WAS 962.9 MILLIBARS /28.44 INCHES/. THIS BREAKS THE PREVIOUS RECORD OF 964.3 MILLIBARS WHICH OCCURRED ON NOVEMBER 10 1998.

PRESSURE RECORDS AT INTERNATIONAL FALLS WERE ONLY AVAILABLE BACK TO 1948. THE LOWEST PRESSURE PREVIOUSLY AT THAT LOCATION WAS 971.9 MILLIBARS ON OCTOBER 10 1949. THE PRESSURE AS OF 1024 AM WAS 967.4 MILLIBARS /28.57 INCHES/. THEREFORE...INTERNATIONAL FALLS ALSO BROKE THEIR PRESSURE RECORD.

THE LOW CONTINUES TO DEEPEN AND THE PRESSURE WILL LIKELY CONTINUE TO FALL. THEREFORE...THIS STATEMENT IS PRELIMINARY AND WILL BE UPDATED ONCE THE LOWEST PRESSURE IS FINALLY OBSERVED. THE LOW WAS AT ABOUT 983 MB ONLY 24 HOURS AGO OVER CENTRAL SOUTH
DAKOTA. THAT IS A PRESSURE DROP OF ABOUT 21 MILLIBARS IN 24 HOURS.

FCST: October 23, KS, NE, IA, MO

TARGET: Redding, IA by 3 p.m. CDT (Albeit family obligations are going to keep me home)

DISCUSSION:
The below water vapor imagery depicts a large trough and several shortwaves that are going to interact with a front and surface low over the central CONUS on Saturday.  One shortwave is visible over northern NM/SE CO with a trailing dryline into the TX panhandle region.  Another impulse just coming ashore on the CA coast.  The right side of the image shows the mid level low in central NE with another front associated with a surface low over northern MN is evident in the northern portion of SD.  The latter is providing the showers we are experiencing in NW MO as I right this blog.



Here is a look at the 0Z/23 surface chart:


Here is the forecasted surface features for Saturday afternoon and evening:



Speed shear dynamics are not lacking with this system but I would like to see some more directional shear at the mid-levels.  Here is a look at the NAM and GFS 250mb charts for 0Z/24.  The ECMWF is for 12Z/23.






Here is a look at the NAM and GFS 500mb chart for 0Z/24:




Helicity values are appreciable in the target area:






Here is a SKEW-T / Hodo from Redding, IA at 23Z/24:



A strengthening low level jet will also be feeding into the area providing a decent moisture transport regime:







SBCAPE from the NAM and GFS:




The last images are forecasted precip from the 4km WRF for 0Z/24 (small caveat: the precip models have not been doing a very good job of late):



All that being said tomorrow has the conditional threat for a severe weather event with all modes of severe weather possible, albeit, the tornadic threat will be early on in the event. The most likely area to see tornadoes is along the IA/MO border where shear and helicity values will be enhanced.

Any existing outflow boundaries from overnight convection and residual cloud cover will have a drastic impact on tomorrow's threat. Throw in the sun angle for late October and it is imperative for clear skies to be around at peak heating to destabilize the atmosphere. As we saw today in TX, OK and KS, a thin veil of 250mb/300mb clouds and lack of any appreciable forcing will make all of the difference between severe weather and a few severe reports and thundershowers. ~ CS