National Weather Service United States Department of Commerce

Mixed Precipitation and Gusty Winds Expected Today

A winter weather and wind advisory is in effect for portions of the North Country today. A wintry mix of precipitation will change to all rain by 10 AM this morning. Gusty winds will develop this morning and continue at times into this afternoon and evening. Isolated power outages and locally slick travel expected. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20250403_0000
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Thu 04/03 00Z 0.26 1720  71  96  -4 0.00
Thu 04/03 01Z 0.29 1624  92  98  -3 0.02
Thu 04/03 02Z 0.33 1630  93  99  -2 0.09
Thu 04/03 03Z 0.34 1732  94  98  -3 0.09
Thu 04/03 04Z 0.35 1737  94  99  -3 0.09
Thu 04/03 05Z 0.29 1739  94  99  -3 0.04
Thu 04/03 06Z 0.23 1841  95  99  -2 0.05
Thu 04/03 07Z 0.18 1845  96  96   0 0.06
Thu 04/03 08Z 0.11 1946  96  96   2 0.09
Thu 04/03 09Z 0.06 1943  96  98   4 0.20
Thu 04/03 12Z 0.13 2047  97  92   7 0.11
Thu 04/03 13Z 0.13 2047  97  93   8 0.04
Thu 04/03 15Z 0.30 2245  92  87  11 0.21
Thu 04/03 16Z 0.39 2248  84  89  12 0.18
Thu 04/03 18Z 0.67 2443  96  46   9 0.10
Thu 04/03 19Z 0.73 2437  98  24   8 0.01
Thu 04/03 20Z 0.91 2436  97  20   7 0.00
Thu 04/03 21Z 1.14 2535  97  28   6 0.03
Thu 04/03 22Z 1.30 2536  85  23   6 0.01
Thu 04/03 23Z 2.09 2539  70  11   6 0.02
Fri 04/04 00Z 3.11 2543  69   1   5 0.02
Fri 04/04 01Z 3.04 2643  82   1   3 0.02
Fri 04/04 02Z 2.54 2640  92   3   2 0.01
Fri 04/04 03Z 1.86 2736  95   6   1 0.00
Fri 04/04 04Z 1.60 2835  90   8   0 0.00
Fri 04/04 05Z 1.72 2836  83  11  -1 0.00
Fri 04/04 06Z 1.27 2933  84  14  -2 0.01
Fri 04/04 07Z 1.12 2931  88  17  -3 0.02
Fri 04/04 08Z 0.93 2929  89  18  -3 0.02
Fri 04/04 09Z 0.82 2930  88  15  -3 0.01
Fri 04/04 10Z 0.74 2930  86   8  -3 0.00
Fri 04/04 11Z 0.65 2929  84   1  -2 0.00
Fri 04/04 12Z 0.61 2930  81   2  -1 0.01
Fri 04/04 13Z 0.60 3031  78   1  -1 0.01
Fri 04/04 14Z 0.56 3030  73   1  -1 0.01
Fri 04/04 15Z 0.52 3029  68   1   0 0.01
Fri 04/04 16Z 0.49 3028  65   1   0 0.01
Fri 04/04 17Z 0.49 3128  64   1   0 0.01
Fri 04/04 18Z 0.51 3128  66   1   0 0.01
Fri 04/04 19Z 0.53 3128  65   1   0 0.01
Fri 04/04 20Z 0.53 3128  63   1   0 0.00
Fri 04/04 21Z 0.50 3228  62   1   0 0.00
Fri 04/04 22Z 0.43 3227  61   2   0 0.00
Fri 04/04 23Z 0.36 3326  61   4   1 0.00
Sat 04/05 00Z 0.28 3424  58   6   2 0.00
Sat 04/05 01Z 0.22 3422  57   7   2 0.00
Sat 04/05 02Z 0.17 3520  54   7   3 0.00
Sat 04/05 03Z 0.10 0018  49   5   3 0.00
Sat 04/05 04Z 0.02 0114  43   7   4 0.00
Sat 04/05 05Z 0.02 0112  41   7   4 0.00
Sat 04/05 06Z 0.03 0307  41   7   4 0.00
Sat 04/05 07Z 0.07 0606  35   6   4 0.00
Sat 04/05 08Z 0.11 0906  29   5   5 0.00
Sat 04/05 09Z 0.13 1207  26   6   5 0.00
Sat 04/05 10Z 0.14 1410  27  13   4 0.00
Sat 04/05 11Z 0.14 1614  30  36   4 0.00

Run total areal avg QPF for the Northern_Greens is: 1.63 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1