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About arlwx

  1. PD3.5 Lite Obs and Nowcasting

    DCA claims it got .42 in precip, but only about .23 of that was listed as snow (actually quite a bit of sleet). So I believe DCA measuring 0.2 snow. At 100 feet here in Arlington, I got a cartopping of sleet, but it looks like the follow-on rain washed that away. DCA stayed at 34 during the snow/sleet part, but sometimes I go out at that temperature and find slick spots. So I believe the measurement of 1.0, map showing it as Grace Hopper Park. (possibly grass/decorator snow).
  2. Weekend Snowfest/Rainfest/Mixed Mess?

    The latest from LWX: .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Surface low pressure will develop over the Tennessee Valley Saturday morning, driven by a digging upper trough flicking across the Great Lakes/Ohio Valley. Transient cold air in place will result in a myriad of precipitation types Saturday afternoon and evening. The latest guidance has trended a little cooler with a little more precipitation, with appreciable snow/sleet amounts of 2-4 inches seeming more likely along the western ridges and the Mason-Dixon line, tapering to an inch or less south of US 50/E of the Blue Ridge, and mainly rain for southern Maryland. Snow-to-liquid ratios are still expected to be below climatology even in areas of all snow due to most of the column where precipitation is developing being above -10 C, though upper jet dynamics could compensate for this somewhat especially over northern Maryland. A light glaze of freezing rain also appears likely for much of the area except northern MD (mainly snow) and extreme southern MD (plain rain). Slightly higher amounts around a tenth of an inch are possible over the central Shenandoah Valley where shallow cold air would be more easily trapped. Surface ridge axis/weak wedge orients itself more or less along I-95 so believe the metros could see a touch of freezing rain as well (usually along this ridge axis is where lower dew points/cooler air pools). Latest guidance is in very good agreement on timing, with little or no precipitation entering the CWA before noon. Clouds and precipitation quickly increase from SW to NE between 1 and 4pm, with the entire area seeing some sort of precipitation by 6 or 7pm. Conditions clear just as quickly around or shortly after midnight, perhaps lingering a few extra hours over the western slopes.
  3. Weekend Snowfest/Rainfest/Mixed Mess?

    The latest from LWX: An upper shortwave diving towards the Gulf of Mexico will be deflected by a strong subtropical ridge, causing it to veer instead towards the Mid-Atlantic. Surface low pressure likely develops over the Tennessee Valley and heads offshore of the Outer Banks of North Carolina by day`s end. Cold air will be in place only briefly, so expect precipitation to start as snow or a snow/sleet mix from SW to NE Saturday midday/afternoon, then change to a mix of rain/sleet and possibly freezing rain. Snow and sleet accumulations should be limited with poor snow-to-liquid ratios (generally an inch or less, except 1-3 for higher elevations and along the Mason-Dixon line). However, this combined with the potential for light icing from patchy freezing rain Saturday evening could still result in slippery travel. The mitigating factor will be warm ground temperatures from several mild days preceding this event. Precipitation should end quickly after midnight as low pressure speeds out to sea. Winds look pretty light late Saturday night, and with temperatures below freezing any residual moisture on the ground will likely turn to ice on untreated surfaces.
  4. February 7th Snow To Rain Event

    So much for the great warmup. As of 2 pm,, DCA managed to get up to 36 degrees.
  5. February 7th Snow To Rain Event

    From LWX: A low pressure system will connect to the tail-end of this warm front Wednesday and move toward the northeast across the region. With a low-level cold air wedge forming on the forward flank of the warm front in our northern and eastern zones, any precipitation that evolves could be in the form of snow or even a wintry mix of snow, sleet and freezing rain. There are uncertainties in types and amounts, so far, and even some discrepancies between the models. All in all, we could be looking at another wintry mess later Tuesday night into Wednesday morning. Eventually rain will overspread the region in the amounts around one quarter to one half inch midday Wednesday into Wednesday afternoon. Seasonable temperatures expected Wednesday.
  6. The latest from LWX: .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... Another cold front along with a potent upper-level trough axis will be fast on the heels of the departing shortwave tonight. This is expected to pass through the Allegheny and Potomac Highlands late this evening...then across the Shenandoah Valley overnight and toward the Washington and Baltimore Metropolitan areas toward Tuesday morning. Frontogenetical forcing along and just ahead of the cold front along with the upper-level trough axis will be enough lift to likely bring a period of snow with the frontal passage. The best chance for a period of snow is expected overnight across the Shenandoah Valley...first thing Tuesday morning for the Washington Metropolitan area...and Tuesday morning for the Baltimore Metropolitan area and for locations near the Bay. For most areas...snowfall accumulations around a coating up to one inch are possible. Did allow for 1-2" near the Mason Dixon line and the far northern/western suburbs of Washington and Baltimore where colder temps will cause higher SLR`s. Either way...aside from the ridge tops most valley locations will be near or above freezing ahead of this system. This combined with the recent warm temps may cause difficulties for snow to stick on paved surfaces. However...strong cold advection behind the boundary will likely cause temps to dip below freezing during the morning rush for the Washington and Baltimore Metropolitan areas. Therefore...any wet or slushy roads do have the chance to freeze during the morning rush. Also...snowfall rates may be moderate to locally heavy for a brief period and if so that can stick on paved surfaces despite the recent warm conditions. Did issue a Winter Weather Advisory for locations along/west of the Allegheny Front where confidence in higher snowfall totals are higher due to an upslope component to the low-level flow. Elsewhere...a Winter Weather Advisory will have to be considered for the Metro areas Tuesday morning but confidence is too low for an advisory at this time.
  7. The latest from LWX: .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/... The rain will continue to gradually taper off from northwest to southeast, however progress will slow considerably as cold front stalls near the Outer Banks and wave low moves along it. The southeastern coastal low will also be moving northeastward and will be near the North Carolina coastline by Monday morning. These features will keep rain chances elevated along the I-95 corridor into this evening and southeast of I-95 well into the night, possibly even into Monday morning across southeast Maryland. Cold air will be gradually filtering into the region, so a few snowflakes are possible across the higher terrain before ending, but no impact expected. Lows by Monday morning will range from the 30s to near 40F. Coastal low will track from near Cape Hatteras Monday morning northeastward well offshore by the evening. An upper level trough carving through the Midwest and Ohio Valley will then move into the region by Monday afternoon, with a strong low level cold front setting up to the west Monday evening. Therefore, Monday should be considerably drier than today, although some showers remain possible, especially across southeast Maryland. Highs generally in the mid/upper 40s. The upper trough will move overhead Monday night into Tuesday morning with the strong low level front crossing the area from 06z to 15z west to east. This will likely bring a period of snow showers to the area, with the potential for some accumulation. Will currently show a coating to up to one inch for much of the area, with 1-2" across some of the higher terrain and for the far northern/western suburbs of Washington/Baltimore into central/northern Maryland. Along and west of the Allegheny Front could see some higher amounts in the westerly upslope flow as well. Temperatures should fall into the 20s to low 30s by morning. Colder and blustery conditions are expected for Tuesday with highs only reaching the 30s. High pressure will build in Tuesday night with clearing skies and lows in the teens to around 20F.
  8. Mid-Atlantic snow totals for winter 2017/18

    Add 0.4 for 1/17 New total: 2.6"
  9. Jan 16/17 light snow event.

    The latest from LWX... (snip) .NEAR TERM /THROUGH WEDNESDAY/... -- Changed Discussion -- Cdfnt will cross the Appalachians later today and slowly progress ewd reaching the I-81 corridor by 00Z Wed. Snow today will fall mainly over the upslope areas of the Appalachians behind the front/wind shift. Some snow could also affect nrn MD counties along the Mason- Dixon line but this is not a done deal as some models and ensemble keep this area dry through much of the day. Tonight and the first half of Wed is when the majority of precip will fall as heights fall in response to approaching upper level trof and forcing for upward vertical motion increases. Deterministic models and their respective ensembles depict precip breaking up as it crosses the mtns with a secondary area of snow over the VA piedmont late tonight into Wed. Ensemble QPF is generally 0.1 to 0.2 inches along and south of the I-64 and west of the I-81 corridors. A big minima or hole in the precip is shown over nrn VA and central MD. Even with these small amounts of QPF, the very cold temperatures will result in SLRs in the order of 15 to 1 and even a little bit of snow potentially causing moderate impacts given sfc temps expected in the mid 20s. It is possible that additional advisories may be needed for the Charlottesville and Fredericksburg areas, but since precip is not expected to begin until late second period or perhaps closer to 12Z Wed decided to hold off on any advisories. Also, our snow probs indicate only a 50% prob of snow exceeding 2 inches and 80% confidence is needed. For the metro areas, the prob of exceeding one inch is about 50-60% which would require an advzy given snow is expected to impact the Wed morning commute, but this is again late second or even third period event. -- End Changed Discussion --
  10. Jan 16/17 light snow event.

    The latest from LWX: .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... A clipper system is expected to cross the Appalachians Tue afternoon. Light snow is expected to develop along the trailing front Tue morning and slowly spread ewd but any precip should remain confined west of the I-81 through 00Z Wed. Heights will then begin to fall rapidly Tue night in response to approaching mid-upper level trof. As heights fall and forcing for upward vertical motion increases, expect snow to spread ewd reaching the I-95 corridor by 12Z Wed. There continues to be some differences with the strength and timing of the upper level system with the Canadian and ECMWF slower and stronger indicating a closed low and the GFS faster and much weaker showing an open trof. As a result, the ECMWF and its ensemble mean show higher QPF generally 0.1 to 0.2 inches while the GFS shows 0.1 inches or less. With the very cold air mass in place, expect SLRs to be higher than climatology in the order of 15 to 1 with snow totals in the 1-2 inch range likely with isold higher totals in the south and over the mtns closer to the track of h5 closed low and in the better moisture. Snow will begin to taper off quickly Wed afternoon with most of the measureable precip gone by 00Z Thu. Advisories will probably be needed for areas west of the Blue Ridge either later today or tonight and Tue or Tue night for areas east of the Blue Ridge.
  11. January Mid-Long Range Disco

    And the GFS call for a storm that none of us here would want (I want the snow to disappear, GFS is calling for an inch).
  12. January Mid-Long Range Disco

    LWX still not sold on a big total: LONG TERM /MONDAY THROUGH FRIDAY/... Alberta clipper will cross the area Tue-Tue night with snow showers possible. The low and associated cdfnt will move offshore by 12Z Wed. A mid-upper level trough over the Great Lks Tue will sharpen as it crosses the mid-Atlc region Wed night. Sfc cyclogenesis has been indicated by Euro/GFS over the past few cycles with the Euro remaining the more consistent model with respect to strength, track, and timing of sfc and upper level features although on this latest cycle the Euro trended drier and faster to move the low out to sea Wed night. A period of light snow remains possible Tue night through Wed night with the best chances of accumulating snow over southeast MD and the eastern shore. Turning brisk on Thu with a warming trend expected to begin next Fri as heights begin to rise over the eastern U.S.
  13. January Mid-Long Range Disco

    I'll worry about the forecast for next weekend once we get past Monday's mess.
  14. January Discobs Thread

    I think there's snow sublimation going on. I couldn't see into my car in Arlington VA this morning, and now I can.
  15. Mid-Atlantic snow totals for winter 2017/18

    Update: 12/30: 0.3" 1/4: 0.7 New total: 2.2"