NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260215_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 02/15 06Z 0.55 3020  85  18 -10 0.00
Sun 02/15 07Z 0.50 3020  87  21 -10 0.00
Sun 02/15 08Z 0.43 3019  88  21 -11 0.00
Sun 02/15 09Z 0.36 3119  90  21 -11 0.00
Sun 02/15 10Z 0.27 3219  86  20 -11 0.00
Sun 02/15 11Z 0.19 3318  76  20 -10 0.00
Sun 02/15 12Z 0.13 3316  62  18 -10 0.00
Sun 02/15 13Z 0.09 3414  49  17  -9 0.00
Sun 02/15 14Z 0.06 3511  40  17  -9 0.00
Sun 02/15 15Z 0.06 0008  34  19  -8 0.00
Sun 02/15 16Z 0.07 0206  32  22  -8 0.00
Sun 02/15 17Z 0.09 0505  31  25  -7 0.00
Sun 02/15 19Z 0.09 1104  32  35  -7 0.00
Sun 02/15 20Z 0.06 1504  33  38  -7 0.00
Sun 02/15 21Z 0.04 1605  31  38  -6 0.00
Sun 02/15 22Z 0.04 1606  28  34  -5 0.00
Sun 02/15 23Z 0.04 1608  28  31  -5 0.00
Mon 02/16 00Z 0.04 1710  30  30  -5 0.00
Mon 02/16 01Z 0.02 1711  31  33  -5 0.00
Mon 02/16 02Z 0.02 1712  36  40  -4 0.00
Mon 02/16 03Z 0.03 1812  43  47  -5 0.00
Mon 02/16 04Z 0.05 1813  52  47  -5 0.00
Mon 02/16 05Z 0.07 1914  65  51  -5 0.00
Mon 02/16 06Z 0.08 1915  76  58  -5 0.00
Mon 02/16 07Z 0.09 1915  84  67  -5 0.00
Mon 02/16 08Z 0.09 1914  87  77  -5 0.00
Mon 02/16 09Z 0.08 1912  87  87  -4 0.00
Mon 02/16 10Z 0.08 1912  88  93  -4 0.00
Mon 02/16 11Z 0.08 1912  89  96  -5 0.00
Mon 02/16 12Z 0.05 1912  90  89  -5 0.00
Mon 02/16 13Z 0.06 1912  91  84  -5 0.00
Mon 02/16 14Z 0.07 1912  92  74  -4 0.00
Mon 02/16 15Z 0.11 2012  92  69  -4 0.00
Mon 02/16 16Z 0.12 2012  93  59  -4 0.00
Mon 02/16 17Z 0.14 2111  93  48  -4 0.00
Mon 02/16 18Z 0.11 2011  93  36  -4 0.00
Mon 02/16 19Z 0.13 2011  93  29  -4 0.00
Mon 02/16 20Z 0.16 2112  93  26  -4 0.00
Mon 02/16 21Z 0.22 2114  93  35  -4 0.00
Mon 02/16 22Z 0.22 2214  93  55  -3 0.00
Mon 02/16 23Z 0.27 2216  94  64  -4 0.00
Tue 02/17 00Z 0.31 2218  94  90  -4 0.00
Tue 02/17 01Z 0.35 2318  92  90  -3 0.00
Tue 02/17 02Z 0.39 2318  91  92  -4 0.00
Tue 02/17 03Z 0.44 2319  95  92  -4 0.01
Tue 02/17 04Z 0.46 2420  97  91  -3 0.02
Tue 02/17 05Z 0.44 2419  97  91  -3 0.03
Tue 02/17 06Z 0.46 2519  97  91  -3 0.04
Tue 02/17 07Z 0.46 2518  96  88  -3 0.03
Tue 02/17 08Z 0.44 2517  96  86  -3 0.02
Tue 02/17 09Z 0.41 2516  95  71  -3 0.02
Tue 02/17 10Z 0.38 2614  96  60  -3 0.01
Tue 02/17 11Z 0.37 2613  97  47  -3 0.01
Tue 02/17 12Z 0.35 2713  97  39  -3 0.01
Tue 02/17 13Z 0.35 2812  97  34  -3 0.02
Tue 02/17 14Z 0.32 2912  97  27  -3 0.01
Tue 02/17 15Z 0.30 2911  97  15  -3 0.01
Tue 02/17 16Z 0.30 2911  96  10  -3 0.01
Tue 02/17 17Z 0.31 2911  96  14  -3 0.01

Run total areal avg QPF for the greens is: 0.26 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