NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260214_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 02/14 12Z 0.39 2816  89  79 -10 0.00
Sat 02/14 13Z 0.44 2818  92  79  -9 0.00
Sat 02/14 14Z 0.44 2818  93  75  -9 0.00
Sat 02/14 15Z 0.44 2816  95  72 -10 0.00
Sat 02/14 16Z 0.41 2915  94  63 -10 0.00
Sat 02/14 17Z 0.43 2914  93  53  -9 0.00
Sat 02/14 18Z 0.55 2915  92  41  -9 0.00
Sat 02/14 19Z 0.67 2815  93  30  -9 0.00
Sat 02/14 20Z 0.79 2816  95  24  -9 0.00
Sat 02/14 21Z 0.79 2817  95  18  -9 0.00
Sat 02/14 22Z 0.85 2819  95  16  -9 0.00
Sat 02/14 23Z 0.83 2821  92  16  -9 0.00
Sun 02/15 00Z 0.73 2923  87  15  -9 0.00
Sun 02/15 01Z 0.67 2924  82  15  -9 0.00
Sun 02/15 02Z 0.63 3025  78  16 -10 0.00
Sun 02/15 03Z 0.63 3025  80  17 -10 0.00
Sun 02/15 04Z 0.65 3025  85  17 -10 0.00
Sun 02/15 05Z 0.66 3026  89  17 -11 0.00
Sun 02/15 06Z 0.53 3126  84  18 -11 0.01
Sun 02/15 07Z 0.43 3127  75  18 -10 0.00
Sun 02/15 08Z 0.34 3128  65  18 -10 0.00
Sun 02/15 09Z 0.25 3228  52  18  -9 0.00
Sun 02/15 10Z 0.17 3227  39  18  -9 0.00
Sun 02/15 11Z 0.11 3325  28  16  -9 0.00
Sun 02/15 12Z 0.06 3421  21  16  -9 0.00
Sun 02/15 13Z 0.05 3517  16  15  -8 0.00
Sun 02/15 14Z 0.09 0112  15  15  -8 0.00
Sun 02/15 15Z 0.11 0209  17  16  -7 0.00
Sun 02/15 16Z 0.13 0408  18  18  -7 0.00
Sun 02/15 17Z 0.09 0504  19  25  -6 0.00
Sun 02/15 18Z 0.08 0704  20  43  -6 0.00
Sun 02/15 19Z 0.09 1004  22  49  -5 0.00
Sun 02/15 20Z 0.04 1404  24  40  -6 0.00
Sun 02/15 21Z 0.01 1706  22  34  -5 0.00
Sun 02/15 22Z 0.02 1708  18  25  -4 0.00
Sun 02/15 23Z 0.05 1810  15  32  -4 0.00
Mon 02/16 00Z 0.07 1811  15  50  -4 0.00
Mon 02/16 01Z 0.07 1811  17  56  -4 0.00
Mon 02/16 02Z 0.08 1811  22  47  -4 0.00
Mon 02/16 03Z 0.06 1812  28  47  -4 0.00
Mon 02/16 04Z 0.11 1814  32  48  -5 0.00
Mon 02/16 05Z 0.12 1914  34  58  -5 0.00
Mon 02/16 06Z 0.13 1915  40  74  -5 0.00
Mon 02/16 07Z 0.10 1814  45  81  -5 0.00
Mon 02/16 08Z 0.06 1813  48  65  -5 0.00
Mon 02/16 09Z 0.06 1812  49  55  -4 0.00
Mon 02/16 10Z 0.06 1811  57  51  -4 0.00
Mon 02/16 11Z 0.04 1811  62  58  -4 0.00
Mon 02/16 12Z 0.04 1712  66  70  -4 0.00
Mon 02/16 13Z 0.05 1812  70  92  -4 0.00
Mon 02/16 14Z 0.05 1811  73  91  -3 0.00
Mon 02/16 15Z 0.06 1810  73  86  -3 0.00
Mon 02/16 16Z 0.06 1809  73  81  -3 0.00
Mon 02/16 17Z 0.05 1809  74  70  -4 0.00
Mon 02/16 18Z 0.06 1808  74  54  -4 0.00
Mon 02/16 19Z 0.07 1906  76  42  -4 0.00
Mon 02/16 20Z 0.08 1906  77  32  -4 0.00
Mon 02/16 21Z 0.08 2006  79  30  -4 0.00
Mon 02/16 22Z 0.08 2005  80  27  -4 0.00
Mon 02/16 23Z 0.10 2006  82  23  -4 0.00

Run total areal avg QPF for the Central_Greens is: 0.01 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