NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260216_0600
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)
=== ===== === ==== ==== === === === ====
Mon 02/16 06Z 0.09 1814  67  38  -7 0.00
Mon 02/16 07Z 0.11 1814  69  46  -6 0.00
Mon 02/16 08Z 0.10 1814  70  52  -6 0.00
Mon 02/16 09Z 0.08 1812  71  57  -5 0.00
Mon 02/16 10Z 0.08 1811  72  73  -5 0.00
Mon 02/16 11Z 0.09 1911  74  83  -5 0.00
Mon 02/16 12Z 0.07 1811  76  83  -4 0.00
Mon 02/16 13Z 0.06 1810  78  84  -4 0.00
Mon 02/16 16Z 0.11 2008  82  68  -4 0.00
Mon 02/16 17Z 0.09 1907  83  63  -4 0.00
Mon 02/16 18Z 0.07 1907  84  60  -4 0.00
Mon 02/16 19Z 0.05 1807  85  53  -4 0.00
Mon 02/16 22Z 0.08 1908  87  40  -4 0.00
Mon 02/16 23Z 0.10 1910  88  34  -4 0.00
Tue 02/17 00Z 0.13 2011  88  27  -3 0.00
Tue 02/17 01Z 0.19 2112  90  27  -3 0.00
Tue 02/17 02Z 0.21 2113  92  33  -3 0.00
Tue 02/17 03Z 0.24 2214  93  40  -3 0.00
Tue 02/17 04Z 0.28 2216  94  80  -3 0.00
Tue 02/17 05Z 0.31 2216  94  88  -3 0.00
Tue 02/17 06Z 0.31 2216  94  89  -3 0.00
Tue 02/17 07Z 0.30 2215  93  90  -3 0.00
Tue 02/17 08Z 0.31 2216  92  97  -3 0.00
Tue 02/17 09Z 0.30 2117  95  97  -3 0.00
Tue 02/17 10Z 0.29 2116  95  98  -2 0.01
Tue 02/17 11Z 0.26 2115  94  96  -2 0.01
Tue 02/17 12Z 0.30 2216  96  91  -3 0.00
Tue 02/17 13Z 0.31 2215  97  72  -3 0.01
Tue 02/17 14Z 0.34 2414  98  63  -3 0.01
Tue 02/17 15Z 0.36 2514  98  46  -3 0.01
Tue 02/17 16Z 0.36 2613  98  33  -3 0.01
Tue 02/17 17Z 0.31 2712  98  24  -3 0.01
Tue 02/17 18Z 0.29 2812  98  26  -3 0.02
Tue 02/17 19Z 0.32 2913  98  25  -3 0.02
Tue 02/17 20Z 0.31 3014  98  15  -3 0.01
Tue 02/17 21Z 0.35 2914  98  12  -3 0.01
Tue 02/17 22Z 0.37 2914  97  14  -3 0.01
Tue 02/17 23Z 0.39 2815  93  13  -3 0.00
Wed 02/18 00Z 0.40 2917  86  13  -3 0.00
Wed 02/18 01Z 0.37 2917  78  12  -3 0.00
Wed 02/18 02Z 0.35 2917  68  10  -3 0.00
Wed 02/18 03Z 0.34 2918  60  10  -2 0.01
Wed 02/18 04Z 0.34 2918  56  13  -3 0.01
Wed 02/18 05Z 0.34 2918  52  12  -3 0.00
Wed 02/18 06Z 0.33 2919  48  14  -3 0.00
Wed 02/18 07Z 0.29 3019  46  16  -3 0.00
Wed 02/18 08Z 0.29 3019  46  19  -3 0.00
Wed 02/18 09Z 0.24 3118  46  28  -2 0.00
Wed 02/18 10Z 0.26 3018  47  46  -2 0.00
Wed 02/18 11Z 0.23 3016  44  52  -2 0.00
Wed 02/18 12Z 0.22 2914  45  62  -2 0.00
Wed 02/18 13Z 0.20 2811  45  81  -2 0.00
Wed 02/18 14Z 0.16 2708  44  83  -2 0.00
Wed 02/18 15Z 0.14 2506  53  85  -2 0.00
Wed 02/18 16Z 0.13 2506  68  92  -2 0.00
Wed 02/18 17Z 0.11 2305  82  92  -3 0.00

Run total areal avg QPF for the Central_Greens is: 0.16 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