WINTER WEATHER: Round 3

Today's blog post is filled with lots of information, so have fun reading!

Think it was cold today?  Well, you would certainly be correct in saying so.  In fact, we have provided two maps from the Oklahoma Mesonet below just to show you how cold it has been. The first shows today's minimum temperatures and the other shows the minimum apparent temperature as a result of strong winds creating bitter wind chill values.  A lot of numbers are missing on the second map due to the fact that some of the Mesonet wind vanes still have ice on them from Tuesday's winter storm, interrupting their functionality.  When temperatures rise above freezing (which won't be until the weekend), the ice will melt, and the vanes will start to function again.

So it snowed on Sunday and Tuesday, and it was bitterly cold today.  Well, now we get the "pleasure" of informing you that these two aspects of winter will come together tomorrow for one chilly, snowy day on Thursday.  This winter storm should not be as large as the previous two but still has the potential to bring some additional snowfall to most of the state.  Here are the latest forecast details.

Tonight and Thursday
PANHANDLE: A 40 percent chance for snow is in place for tonight.  Low temperatures will fall to the low single-digits, or even slightly into the negatives by a degree or two.  A northeast wind will blow between 5 and 10 mph, creating wind chills between the -10 and -15 degree range.  For Thursday, light snow will be possible through early morning; otherwise, skies will remain cloudy for the remainder of the day.  Highs will rise to the mid-teens.  Winds will shift to the south-southeast and blow between 5 and 10 mph, with wind chill values between -5 and -15 degrees.  Only a dusting of snow is forecast through Thursday with this storm system.
ALERTS IN EFFECT: WIND CHILL ADVISORY

NORTHWEST: Snow will begin after midnight tonight and last through early morning Thursday before tapering off.  The best chances for snow and accumulation will be towards the south end of this region.  Areas near the border will see a lesser chance for snow and little to no accumulation.  Farther south, between 1 and 2 inches of snow is expected.  Lows tonight will fall to the lower-and-mid single-digit range, with highs rising to the mid-teens on Thursday.  Winds tonight will blow between 5 and 15 mph from the north, with gusts as high as 20 mph.  Wind chills will be as cold as -10 degrees.  On Thursday, winds will blow generally from the northeast between 5 and 10 mph.  Wind chill values will be as cold as -15 degrees, especially earlier in the day.
ALERTS IN EFFECT: WINTER WEATHER ADVISORY (south), WIND CHILL ADVISORY

SOUTHWEST: Beginning later this evening and lasting through Thursday morning before ending in the afternoon, snow is likely across the region, especially farther south and west.  Here, accumulations could total 2 to 3 inches, with accumulations of 1 to 2 inches elsewhere across the region.  Lows tonight will drop to the upper single-digits, with highs on Thursday reaching the mid-to-upper-teens.  A brisk north wind will blow between 10 and 20 mph tonight, with gusts as high as 25 mph.  Wind chill values will be as low as -10 degrees.  For Thursday, winds will blow between 5 and 15 mph, with gusts up to 20 mph.  Wind chill values will again be as low as -10 degrees, especially for the earlier part of the day.
ALERTS IN EFFECT: WINTER WEATHER ADVISORY, WIND CHILL ADVISORY

NORTH CENTRAL: A slight chance for snow exists tonight after midnight, with slightly higher chances tomorrow morning.  Lows tonight will fall to the lower-to-mid-single-digits.  Wind chill values will be as low as the -10 to -15 degree range as winds blow from the north between 10 and 15 mph, gusting up to 20 mph.  For Thursday, a chance for snow is forecast through the morning, with skies remaining generally cloudy for the remainder of the afternoon.  Highs will be in the mid-teens.  Wind chills will as cold as -15 degrees.  A north wind will blow around 10 mph.  Accumulations in this region will be a dusting to 1 inch.
ALERTS IN EFFECT: WIND CHILL ADVISORY

CENTRAL: Snow will begin after midnight tonight, with the greatest chances south of the Oklahoma City metro.  The snow will last through about noon to early-afternoon on Thursday, with some moderate snowfall possible during the morning hours.  Accumulations will be between 2 and 3 inches in areas towards the far west of the region, while totaling 1 to 2 inches for the remainder of the region.  Lows tonight will fall to the mid-to-upper single-digits, with highs on Thursday rising to only the mid-teens.  With a north wind blowing between 10 and 15 mph tonight and tomorrow, expect wind chill values as cold as -10 degrees.
ALERTS IN EFFECT: WINTER WEATHER ADVISORY, WIND CHILL ADVISORY

SOUTH CENTRAL: Snow will also begin to impact this region beginning after midnight as clouds increase.  Moderate snow is possible from the early morning hours on Thursday through the early afternoon before tapering off.  Total accumulations will generally be around 1 inch, with higher amounts towards the northern end of the region.  While lows tonight fall to the low-teens, highs tomorrow will rise to the low-20s.  A northeast wind will blow between 10 and 15 mph tonight and diminish to 5 to 10 mph tomorrow.  Wind chill values will be as cold as -5 degrees.
ALERTS IN EFFECT: WINTER WEATHER ADVISORY, WIND CHILL ADVISORY

NORTHEAST: The next round of winter weather will not bring significant impacts to northeastern Oklahoma.  A slight chance for snow is forecast from early Thursday morning through mid-afternoon.  Chances are higher farther towards the south and west of the region.  Accumulations will remain minimal.  Lows will fall to the middle single-digits.  With a north wind blowing between 10 and 15 mph, expect wind chill values between -5 and 0 degrees.  Highs on Thursday will rise to the mid-teens, with wind chill values as cold as -10 degrees as a north wind blows between 5 and 10 mph.
ALERTS IN EFFECT: WIND CHILL ADVISORY

SOUTHEAST: Beginning in the early morning, there exists a chance for snow, with higher chances throughout the morning hours, especially farther north.  The snow will last through early evening.  Accumulations of 1 to 3 inches are possible towards the northern end of the region.  Lows tonight will drop to the low-to-upper-teens, with Thursday's highs rising to the low-to-mid-20s.  Wind chill values will generally be between 0 and 10 degrees as a north wind blows between 5 and 15 mph.
ALERTS IN EFFECT: WINTER WEATHER ADVISORY (north), WIND CHILL ADVISORY (north)

Flashback: Tuesday's Winter Storm
It's time for a quick meteorology lesson!  Tuesday's winter storm brought a large swath of snow to northern parts of the state and more even to Kansas and Nebraska, but none to very little across central and southern Oklahoma.  Forecasts did call for less amounts of snow in these regions, but even areas in central Oklahoma south of the Oklahoma City metro which could have received up to 1 inch of snow received almost nothing but a freezing rain/sleet mix through the early morning hours.  So why the lack of snow in a region which picked up as much as 4 to 6 inches only a couple of days earlier?  Well, there are two reasons for this.  The first concerns the air temperatures, both at the surface and at upper-levels of the atmosphere.  We introduced the atmospheric sounding in one of our blog posts from December of last year.  You can visit this post to get a quick refresher course.

The atmospheric sounding for Norman, OK from Tuesday morning at 12Z (6 AM CST) is shown to the right.  You will notice how the red and green lines (the temperature and dew point profiles, respectively) are overlapping each other, indicating that the air is moist and supportive of precipitation.  However, the lines are both riding very closely on the rightmost blue dashed line, which represents freezing (0°C or 32°F).  In fact, the lines cross slightly to the right of the blue line at one point.  Even though this happens for only a relatively short distance (in meteorological terms), the slight melting above the surface, combined with a surface temperature almost right at freezing, caused freezing rain or sleet to be the dominant precipitation type across the region because the atmosphere simply wasn't cool enough to support snow crystals falling towards the ground.

So that solves the freezing rain/sleet/snow mystery, but why did the precipitation seem to last for a shorter period of time?  Well, this has to do with what meteorologists call a dry slot.  According to the National Weather Service, the dry slot is:

A zone of dry (and relatively cloud-free) air which wraps east- or northeastward into the southern and eastern parts of a synoptic scale or mesoscale low pressure system. A dry slot generally is seen best on satellite photographs.

The dry slot caused abundant precipitation in areas towards the north and east of the central Oklahoma region, while cutting off precipitation in central Oklahoma itself.  The two graphics shown demonstrate the dry slot.  The first, provided by the Oklahoma Mesonet, is from the actual storm on Tuesday.  The second, provided by Luke Madaus, is only an example and not from Tuesday's storm.







Below is an animated GIF showing NWS Norman's snowfall forecasts, from the first-issued forecast to the actual amounts.

 

AC

Forecasts based on the National Weather Service.  Please visit NWS Amarillo (OK panhandle), NWS Norman (central/western OK), and NWS Tulsa (eastern OK) for additional up-to-date details.

Additional Sources: OK Mesonet (temperature graphics and dry slot image), Luke Madaus (dry slot example), Google Images (photo)