Monday, February 18, 2019

Some Weather and Climate Anomaly News: An Impending DMV Area Wintry Mess and 2018 Record Rainfall Report; Las Vegas Rare and Maui Exceptionally Rare Accumulating Snowfalls

Snowy sunset, Frederick, Md., Jan 29, 2019; Photo by Instagram user Alex Turner.

This picture was featured in a Capital Weather Gang entry late last month after a snowfall. (I don't have the link immediately available.)

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It's time, I guess, for another entry. I didn't post one, as I suggested I would, in the wee hours of Sunday. Instead of a personal update, however, this entry is a weather and climate anomaly update …

Sterling (LWX) county warning area (CWA) advisories updated 10:06 p.m. EST Feb 18, 2019

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There is a winter storm watch in effect for the "DMV" -- Metro D.C. and Baltimore areas -- ahead of a system that is forecasted to bring a burst of heavy snow followed by a wintry mix of sleet and freezing rain before turning to all-rain as it ends.

U.S. NWS weather advisories (without legend), updated 0328 UTC 19 Feb 2019 (10:28 p.m. EST Feb 18, 2019)

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A low pressure system is forecasted to organize in the Gulf of Mexico along a stalled out frontal boundary and push north-northeastward up the Mississippi River Valley with abundant Gulf moisture.

NWS/WPC/NDFD U.S. surface weather map forecast showing isobars, fronts, and type and likelihood of precipitation for 12Z 19 Feb 2019

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Even in the wintertime, this set up would normally bring rain to the East Coast coastal plain, but there is a sprawling 1040mb Arctic high pushing eastward from the Upper Great Plains across the Great Lakes and into New England.

NWS/WPC/NDFD U.S. surface weather map forecast showing isobars, fronts, and type and likelihood of precipitation for 0Z 20 Feb 2019

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This high should cause a cold air damming situation that lasts long enough to keep the precipitation frozen across the D.C. and Baltimore areas to bring accumulating snow and then sleet and a glaze of freezing rain.

NWS/WPC/NDFD U.S. surface weather map forecast showing isobars, fronts, and type and likelihood of precipitation for 12Z 20 Feb 2019

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Of course, if the punch of warm air is strong enough or if the precipitation axis sets up north of the D.C. area, the forecasted amounts of 4 to 8 inches could be a lot less, especially here in the District proper.

NWS/WPC/NDFD U.S. surface weather map forecast showing isobars, fronts, and type and likelihood of precipitation for 0Z 21 Feb 2019

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In fact, that is the thinking of the Capital Weather Gang's Wes Junker in this entry (link embedded): Wednesday's winter storm: Here's how much snow and ice to expect and when. For that reason, CWG has lower amounts forecasted than the National Weather Service (as issued by the Baltimore/Washington NWSFO, a.k.a., Sterling (LWX)).

CWG snowfall forecast map for the "DMV" region for February 20, 2019

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Nevertheless, Sterling acknowledged this is in its area forecast discussion:

The snow may be heavy at times thanks to the strong low level jet and frontogenesis in the 850-700 mb levels, and this could put down a quick 4-8 inch snowfall thanks to the copious Gulf moisture available. After that, the warm air aloft will overwhelm the region, with snow change to sleet and freezing rain from south to north during the midday and afternoon hours.

Sterling (LWX) CWA expected snow forecast map,
valid 7 p.m. EST 19 Feb - 7 p.m. EST 20 Feb 2019, issued 10:07 p.m. 2/18/2019

This is significantly reduced from the forecasted amounts earlier today -- especially for areas in the Blue Ridge / Shenandoah.

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Sterling (LWX) CWA ice accumulation forecast map,
valid 7 a.m. EST 20 Feb - 7 a.m. EST 21 Feb 2019, issued 10:13 p.m. 2/18/2019

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Continued LWX area forecast discussion excerpt:

Overall expect the warm air aloft to be a bit stronger than earlier guidance suggested, so cut snow amounts a bit, while increasing ice amounts a bit, but there are still details to be worked out. If the snow lingers longer, it could be quite heavy, so amounts could be several inches low. If, conversely, the warm advection aloft proves stronger than modeled (not an atypical situation), our snow amounts could prove too high across much of the region.

Winter Storm Severity Index (experimental) valid through 7 a.m. EST Feb 21, 2019; Click on image for a larger version

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Anyway, the primary low will push into the Great Lakes as a secondary coastal low forms off the Mid-Atlantic -- if only because of such a strongly baroclinic zone just offshore -- but that low isn't forecasted to bring any additional snow / mixed precipitation.

Thereafter, the pattern looks like it will shift to a relatively mild one for the remainder of February.

Regardless, KDCA itself should get at least the 1.4 inches needed to bring the seasonal total to the 30-year annual average of 15.4 inches -- and thus avoid another below-normal snowfall year.

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NWS/NCEP/WPC 3-day quantitative precipitation forecast (QPF) for the Lower 48 U.S.,
valid 0Z 19 Feb 2019 - 0Z 22 Feb 2019

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I'd like to note that Sterling LWX just issued a comprehensive report on the tremendous rainfall totals of 2018 to include the image directly below (see caption). The report is available here (link embedded): Record Rain and Flooding of 2018.


This page includes a series of tabs to links:

* Overview
* Baltimore & Washington Rainfall Statistics
* Other Precip Totals
* Flood Explorer Maps
* Significant Floods Recap

It includes the following introduction:

2018 was a memorable year for the Mid-Atlantic region, with some of the most frequent and persistent flooding observed in many years. While the severity of the flooding was not record breaking, the persistent nature of the rain kept conditions primed for flooding for about 75% of the year.

This page looks back at the significant and record-breaking rainfall from 2018, as well as the numerous flood events which occurred. Not all flood events are represented here; only the most significant are included.

Below is a map showing estimated rainfall (and melted snowfall) from the entire year. Click on it to make it larger:


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Some other weather news items …

It continues to be very wet on the West Coast, especially in California to include the Los Angeles area and parts of the Desert Southwest.

List of most consecutive days with precipitation in Las Vegas; Source: NWSFO Las Vegas tweet, Feb 18, 2019.

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Through Feb 18th, Las Vegas has had unusual five-day stretch with measurable precipitation each day -- tying for the second-longest such stretch just beyond six days (set in 1943 and again in 2003 (see image directly above).

Las Vegas snowfall amounts for Feb 18, 2019; Source: NWSFO Las Vegas tweet, Feb 18, 2019.

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This precipitation has included both rain and snow -- and while only "trace" was recorded at McCarran Int'l Airport (KLAS) -- there was 1 to 2 inches in other parts of Las Vegas Three was also 3.5 inches at Mount Charleston (an 11,916'  foot peak about 40 miles NW of the Strip). The Los Angeles Times had this article: It just snowed in Vegas and likely will again this week. That isn't normal.

Children in the West Summerlin neighborhood playing in a rare Las Vegas snowfall; photo from the Las Vegas Review Journal, Feb 18, 2019

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The article notes:

In 2008, the airport got more than 3 inches. That dump caused delays to flights because of low visibility, and stranded some travelers overnight.

But snowfall totals like those in 2008 are unusual for Las Vegas.

This month, snow has fallen on Las Vegas already -- though not with the totals seen Sunday night. And multiple snow days in February are not common.

Since 1939, February has seen more than three snowfall days only twice -- the last time in 1949. The latest that snow ever fell in Las Vegas in a winter was March 3, 1976 …

This CWG entry added that the snowfall marks the first time that KLAS has recorded multiple days of measurable snow in the same month since February of 1987.

Snow-covers the top of Haleakalā on Maui, Feb 11, 2019

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The LA Times article also noted the unusually low-elevation snowfall that occurred in the Hawaiian Islands. This snowfall was associated with an exceptionally powerful storm system -- known as a "Kona low" -- that brought a 191 mph wind gust atop Mauna Kea and snow levels as low as 6,200 feet on Maui, specifically, the Polipoli Spring State Recreation Area. There was about 6 inches of snow recorded atop Haleakalā, a 10,023-foot peak on Maui.

Another image of the snow-blanketed top of Haleakalā on Maui, Feb 11, 2019; source here.

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To be clear, wintertime snow is common atop Mauna Loa and Mauna Kea on the Big Island, but no where else in the Hawaiian Islands.

And with that, I'll end this entry.

--Regulus

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