Wednesday, April 20, 2011

Hitting the bull's-eye

The snow came to an end by Wednesday afternoon across the Twin Cities metro, and we were able to get sunshine to break out for a few hours to help erase the vision of April snow.  A few instability showers popped up towards the evening commute, but nothing that caused a great deal of inconvenience.

Tuesday night, I forecasted a 1 to 3 inch range of snow totals, and by golly, it looks like I hit the nail right on the head.  Here is a listing of snow fall reports across the area:

IN.  LOCATION                ST COUNTY      TIME
---- ----------------------- -- ----------- -------
3.00 1 SSE CLEAR LAKE        MN SHERBURNE   0806 AM
3.00 PLYMOUTH                MN HENNEPIN    0759 AM
2.50 6 NW RICE LAKE          WI BARRON      0936 AM
2.50 2 ENE PLYMOUTH          MN HENNEPIN    0800 AM
2.40 SAUK RAPIDS             MN BENTON      0642 AM
2.20 FRIDLEY                 MN ANOKA       1016 AM
2.20 NEW HOPE                MN ENNEPIN     0806 AM
2.20 BUFFALO                 MN WRIGHT      0630 AM
2.00 ST CLOUD AIRPORT        MN STEARNS     0100 PM
2.00 CLAYTON                 WI POLK        1016 AM
2.00 4 E ST FRANCIS          MN ANOKA       0730 AM
2.00 KIMBALL                 MN STEARNS     0643 AM
1.90 5 NE FOREST LAKE        MN CHISAGO     0700 AM
1.70 3 WNW RICE              MN STEARNS     0700 AM
1.70 ELK MOUND               WI DUNN        0700 AM
1.70 RICE                    MN BENTON      0700 AM
1.60 1 ENE ST MICHAEL        MN WRIGHT      0700 AM
1.60 1 NNW NORTH ST PAUL     MN RAMSEY      0700 AM
1.50 STANLEY                 WI CHIPPEWA    0800 AM
1.50 AUGUSTA                 WI EAU CLAIRE  0800 AM
1.50 1 SSW RIVER FALLS       WI PIERCE      0705 AM
1.50 2 SE CHETEK             WI BARRON      0700 AM
1.40 ONAMIA                  MN MILLE LACS  0830 AM
1.40 1 NW ISANTI             MN ISANTI      0600 AM
1.30 CHANHASSEN NWS          MN CARVER      0100 PM
1.30 FARMINGTON CWSU         MN DAKOTA      1100 AM
1.30 ROBERTS                 WI ST. CROIX   0800 AM
1.30 1 WSW LITTLE CANADA     MN RAMSEY      0700 AM
1.20 HAMMOND                 WI ST. CROIX   0700 AM
1.20 JIM FALLS               WI CHIPPEWA    0630 AM
1.20 6 WNW ELLSWORTH         WI PIERCE      0600 AM
1.10 1 SW EDINA              MN HENNEPIN    0730 AM
1.10 4 SE MAPLEWOOD          MN WASHINGTON  0700 AM
1.10 MORA                    MN KANABEC     0700 AM
1.00 WELLS                   MN FARIBAULT   0800 AM
1.00 ALBERT LEA              MN FREEBORN    0800 AM
1.00 LITCHFIELD              MN MEEKER      0800 AM
1.00 STILLWATER              MN WASHINGTON  0800 AM
1.00 RICE LAKE               WI BARRON      0800 AM
1.00 3 SE LAKE ELMO          MN WASHINGTON  0800 AM
1.00 WINNEBAGO               MN FARIBAULT   0800 AM
1.00 MILACA                  MN MILLE LACS  0730 AM
1.00 ST CROIX FALLS          WI POLK        0700 AM
1.00 HOLCOMBE                WI CHIPPEWA    0700 AM
1.00 ELLENDALE               MN STEELE      0700 AM
1.00 LONG LAKE               MN HENNEPIN    0700 AM
1.00 BALDWIN                 WI ST. CROIX   0700 AM
1.00 ZUMBROTA                MN GOODHUE     0700 AM
1.00 ELK RIVER               MN SHERBURNE   0700 AM
1.00 9 NNE BIRD ISLAND       MN RENVILLE    0645 AM
1.00 LITCHFIELD              MN MEEKER      0630 AM

Thankfully, I do not see any more significant snows on the horizon.  Hopefully anything that falls out of the sky going forward is rain.  I think it’s safe to say we’ve all had it with the snow.  It’s time to bring on spring.  We’ve been officially in spring for a month.  Now the temperatures and precip type need to start feeling like it!


Tuesday, April 19, 2011

More April snow. Ugh.

A low pressure system out of the Rockies will move through Illinois by late Tuesday, bringing with it precipitation that will fall mainly as rain during most of the day Tuesday before some snow mixes in Tuesday night as cold air wraps around the backside of the low.  Yes, we are not through with snow in April folks.  Old Man Winter still wants one last laugh before we transition to spring.  This is the 4th snowiest seasonal snowfall on record, and we are just 3.7 inches away from taking over 3rd place.

Looking at the 00z NAM model data, it appears the snow will begin to fall between 7-9 PM Tuesday and be continuous through the afternoon on Wednesday.  Liquid precip amounts will be running around .35 inches.  Using a 8-to-1 snow ratio average, it equates out to roughly 3 inches of snow, which will be the high end of the snow total range.


Looking at all the available model output, the general consensus seems to be from 1 to 3 inches of snow across the Twin Cities metro.  Since temperatures will be hovering right around freezing, we will not see fluffy snow.  Just some thick, wet flakes as the changeover happens from rain to snow.


The Wednesday morning commute could be a little slow, as the GFS model advertises the heaviest of the snowfall will occur.  The temperature profile below at 7 AM Wednesday shows all layers of the atmosphere below freezing (0°C) all the way up to 25,000 feet above the earth’s surface.  That’s impressive for this time of the year!


To wrap this up, I’m expecting 1-3 inches of snow for the metro with heavier amounts across southeast Minnesota, where they could be closer to the 4-6 inch snowfall range.  Places such as Red Wing, Rochester, and towards La Crosse, Wisconsin.  Spring is being casually late this year due in part to the La Nina winter we experienced.  With the effects of La Nina diminishing, hopefully we will find some balance and that our summer will be beautiful.  Still too early to say for sure, but my hunch is that the middle part of summer could very well be hot and dry.  Something I will keep my eye on, that’s for sure.  We’ll make it through this.

Latest watches and advisories:
Winter Weather Advisory valid at Apr 19, 7:00 PM CDT for Anoka, Blue Earth, Brown, Carver, Chisago, Dakota, Faribault, Freeborn, Goodhue, Hennepin, Le Sueur, Martin, McLeod, Nicollet, Ramsey, Rice, Scott, Sibley, Steele, Waseca, Washington, Watonwan [MN] and Barron, Chippewa, Dunn, Eau Claire, Pepin, Pierce, Polk, Rusk, St. Croix [WI] till Apr 20, 12:00 PM CDT


Wednesday, April 13, 2011

04.10.11 Chase: Western WI

My first chase of the 2011 severe thunderstorm season took place on Sunday, April 10.  I had been anticipating a tornado outbreak to occur several days in advance as all the dynamics were coming together to set the stage for explosive thunderstorm development with enough wind shear for tornado development.  In the end, the day turned out to be a bit of a bust as storms failed to muster anything noteworthy in my target area.

The Storm Prediction Center (SPC) had put out a moderate risk of severe weather in the early morning hours for much of Wisconsin into northern Illinois during the day on Sunday, primarily for large hail and possibility of strong tornadoes.


Here was the surface setup at 7:15 AM (1215Z) Sunday morning.  The low pressure center with adjacent warm front extended from the Minnesota/Iowa border with a trailing cold front across western Iowa.


Based on the tornado parameters I was seeing, and knowing that any storms would be racing to the east-northeast very quickly (nearly 60 MPH!) along with the High Resolution Rapid Refresh (HRRR) forecast model showing storm development in southeast Minnesota and western Wisconsin, I chose to chase in an area between Hudson, WI, Menomonie, WI, and Red Wing, MN.


Shortly after 2 PM after stopping at my parents’ place for lunch, I set forth on the road towards Wisconsin.  I arrived in Roberts, WI, just north of Interstate 94 shortly after 3 PM to await storm initiation, and to get my live dash camera rolling.  As I was driving east, one thing concerned me and that was the cloud cover.  I never seemed to get completely away from it and that really prevented surface heating from happening.  Cloud tops also had a “milky” appearance to them, which is a sign that instability isn’t great for severe storms.  Here is a satellite image and associated cloud cover 2:15 PM, which was put together by Paul Huttner on his Sunday, April 10, blog post.  Western Wisconsin broke out into the 70’s for temperatures, but pesky cloud cover really prevented the trigger for strong storm development in my view.


Storms begin to fire along the cold front near Red Wing, MN around 3:08 PM, as depicted on National Weather Service radar from Minneapolis.


Shortly after, a tornado watch with particularly dangerous situation (PDS) emphasis was issued at 3:20 PM by the SPC in anticipation for a widespread tornado outbreak.


Here is radar for the duration of my time chasing out in Wisconsin.  Going in with the mindset that it was going to be a bad day based on the cloud cover and the storms moving like rockets, I decided to make this a short chase.  There was no severe weather reports associated with any storms until one inch hail was reported in Spring Valley, WI around 3:30 PM and some smaller reports of hail around Menomonie between 4:30 and 4:45 PM.  I generally worked the southwest side of the storm cell I was chasing to watch for tornado development instead of punching the core and being hailed on.  If I want to chase ice cubes, I would go after the refrigerator in the kitchen.  I did find it difficult to keep up with the speed the storms were moving at and also ran into data dead zones, which prevented me from picking up updated radar images.  Keep getting behind the storms and when I did catch up, all I experienced was rain.  I ended my chase shortly before 5 PM in Menomonie, where temperatures reached 80 degrees before the rain moved in, knowing not much was going to take place.  The storms would eventually become tornadic east of Eau Claire in Augusta, where two EF-1 tornadoes touched down on the west and north side of town.


It was a disappointing chase, but I’m also glad the storms were not worse.  I encountered college students at UW-Stout, horseback riders, and walkers out enjoying the warm day.  Given how rapidly these storms could have intensified and fast movement, people would had little opportunity to find shelter.  This could have been a much disastrous situation.  Here is a GPS plot of the area I chased this day.  I managed to determine the area where the storms would be, but were not of any significance.  I had mixed thoughts on this chase.  It was good to finally see some storms, however with gas prices climbing, I may need to be more selective with which storms I chase, and how far I travel this year.  Storm chasing is definitely not a cheap hobby!


All the media I got from this storm is one photo of clouds heading back home west on I-94 from Menomonie.



Sunday, April 10, 2011

Storms ending; quiet week ahead after an active weekend

Severe storms will continue to push through Wisconsin tonight as a cold front progresses towards the east putting an end to all the rough weather this weekend, including a devastating tornado outbreak in Iowa on Saturday.  Behind the front is much cooler and stable air.  Just to describe the contrast, at 2 PM, the temperature at MSP was 75 degrees, which was also the high temperature for the day.  Three hours later, the temperature dropped 17 degrees, to 58.  We should get back into the 60s by Tuesday with temperatures above 50 degrees most of the week.


The week will finish on a wet note as a storm system comes into the area, bringing with it abundant moisture with close to two inches of perceptible liquid as indicated by the GFS model.  Yes, we could also be dealing with snow by Thursday into Saturday as temperatures are cooler in the upper levels of the atmosphere.  Just when you thought the snow is done with, it’s a reminder it’s still April, and this is not unusual for this time of the year.


Have a good week!


Severe Storm Sunday

Another day, another chance of severe thunderstorms across the area.  A moderate risk of thunderstorms is in play today for the eastern Twin Cities metro east into most of Wisconsin, with a slight risk of severe weather for the central part of the country.  I’m expecting a pretty rough day for our friends on the other side of the St. Croix River, with large hail and perhaps strong tornadoes.


Strong instabilityCAPE values, which I described a little bit about yesterday, will be around 2000-3000 J/kg across the moderate risk area, which is quite strong for this time of the year.  Another parameter I use in forecasting is the Energy Helicity Index (EHI). It combines instability and wind shear to come up with a value where tornado development will be the greatest.  Almost like a tornado probability scale if you will.  It appears the area just east of the St. Croix will be prime for supercells near the warm front.  The maps below from Twister Data are from 3 PM today, showing the most favorable environment for storm initiation:



Expecting another very active day for our area and you’ll want to pay attention to watches and warnings issued as storms may fire and move very quickly today.  Stay safe!


Friday, April 8, 2011

First severe thunderstorm threat for the Upper Midwest this weekend

Our first bout of severe weather this year is possible this weekend across many areas of the Upper Midwest as a low pressure system moves in overhead from Nebraska.  A warm front draped across Iowa will move northward, drawing up very warm temperatures with readings near 70 degrees, and dew points approaching 60 degrees.  Severe weather is possible both days with the slow moving warm front, but I’m anticipating Sunday to have the greatest severe storm potential.  All the dynamics are coming together in the upper and lower levels of the atmosphere for a significant severe weather outbreak across several states, including Minnesota.

A tornado threat will exist near the Mississippi River valley Sunday as wind shear will be quite strong - change in direction with height.


Here are the parameters why I’m liking the severe storm chances on Sunday based on the latest NAM models:

Convective Available Potential Energy (CAPE) values will be well above 1000 joules per kilogram, which is often used as the threshold for thunderstorm development.  CAPE indicates the amount of energy available for convection.  The higher the number, the greater the potential for severe weather.  Far southeast Minnesota, eastern Iowa, most of Illinois, and southern Wisconsin are under the gun for the most active weather.  Here are the CAPE values as of 4 PM Sunday:


Another reason why I favor the above area for severe weather are the lapse rates.  Lapse rates are the change in temperature with height in the atmosphere.  Steep lapse rates, where there is the greatest cooling with height will be found across Iowa into southeastern Minnesota.


With steep lapse rates, also correlates with a weak cap, which will allow for thunderstorm development.  A cap, or lid, is warm air aloft that prevents storm development since air particles are restricted from rising to create the large cumulonimbus clouds that form thunderstorms.  The cap is the weakest across southeast Minnesota along the Mississippi River into southwest Wisconsin and northern Iowa.


This is shaping up to be quite a stormy weekend.  If you have outdoor interests, I would advise to have a plan B and pay attention to the skies.  If you see any towering cumulonimbus clouds, it’s a sure sign bad weather is on it’s way.  Be safe this weekend and stay tuned for additional updates!