NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260411_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)
=== ===== === ==== ==== === === === ====
Sat 04/11 06Z 0.30 3118  98  89   0 0.00
Sat 04/11 07Z 0.39 3121  92  77   0 0.01
Sat 04/11 08Z 0.40 3123  90  66  -2 0.01
Sat 04/11 09Z 0.49 3126  90  24  -3 0.01
Sat 04/11 10Z 0.58 3128  91   5  -4 0.01
Sat 04/11 11Z 0.64 3129  93   2  -5 0.00
Sat 04/11 12Z 0.77 3129  93   5  -6 0.00
Sat 04/11 13Z 0.97 3128  94   7  -7 0.00
Sat 04/11 14Z 0.99 3128  91   9  -7 0.00
Sat 04/11 15Z 1.09 3126  88   8  -7 0.00
Sat 04/11 16Z 1.30 3124  86  10  -7 0.00
Sat 04/11 17Z 2.55 3121  84  11  -7 0.00
Sat 04/11 18Z 4.96 3120  82  12  -7 0.00
Sat 04/11 19Z 5.93 3118  79  12  -6 0.00
Sat 04/11 20Z 6.36 3118  78  12  -6 0.00
Sat 04/11 21Z 6.16 3118  76  11  -5 0.00
Sat 04/11 22Z 5.49 3119  75  10  -5 0.00
Sat 04/11 23Z 3.58 3121  75   9  -6 0.00
Sun 04/12 00Z 1.84 3123  76  10  -6 0.00
Sun 04/12 01Z 1.30 3125  78  10  -6 0.00
Sun 04/12 02Z 0.85 3226  80  12  -6 0.00
Sun 04/12 03Z 0.87 3228  79  12  -6 0.00
Sun 04/12 04Z 0.59 3228  75  12  -6 0.00
Sun 04/12 05Z 0.36 3327  70  13  -6 0.00
Sun 04/12 06Z 0.24 3326  65  14  -6 0.00
Sun 04/12 07Z 0.13 3424  63  14  -5 0.00
Sun 04/12 08Z 0.09 3421  65  13  -5 0.00
Sun 04/12 09Z 0.07 3417  65  16  -5 0.00
Sun 04/12 10Z 0.06 3414  61  17  -4 0.00
Sun 04/12 11Z 0.05 3311  57  17  -3 0.00
Sun 04/12 12Z 0.07 3208  53  19  -2 0.00
Sun 04/12 13Z 0.08 3005  49  20  -1 0.00
Sun 04/12 14Z 0.08 2603  43  20   0 0.00
Sun 04/12 15Z 0.10 2304  40  25   0 0.00
Sun 04/12 16Z 0.16 2206  43  33   0 0.00
Sun 04/12 17Z 0.24 2108  41  38   0 0.00
Sun 04/12 18Z 0.61 2109  43  57  -1 0.00
Sun 04/12 19Z 0.29 2011  35  85   0 0.00
Sun 04/12 20Z 0.22 1914  31  95   0 0.00
Sun 04/12 21Z 0.30 1918  36  93   0 0.00
Sun 04/12 22Z 0.31 1920  35  94   1 0.00
Sun 04/12 23Z 0.47 2024  44  98   1 0.00
Mon 04/13 00Z 0.53 2025  65  97   0 0.01
Mon 04/13 01Z 0.49 2029  78  98   0 0.02
Mon 04/13 02Z 0.46 2130  90  98   2 0.03
Mon 04/13 03Z 0.48 2134  95  98   4 0.08
Mon 04/13 04Z 0.50 2136  95  97   6 0.06
Mon 04/13 05Z 0.60 2242  96  95   7 0.11
Mon 04/13 06Z 0.71 2347  96  95   8 0.13
Mon 04/13 07Z 0.78 2449  96  93   9 0.11
Mon 04/13 08Z 0.80 2549  96  92  10 0.05
Mon 04/13 09Z 0.83 2549  96  91  10 0.05
Mon 04/13 10Z 0.83 2548  95  89  10 0.04
Mon 04/13 11Z 0.84 2647  95  90  10 0.03
Mon 04/13 12Z 0.85 2647  94  89  10 0.02
Mon 04/13 13Z 0.91 2648  95  92  10 0.03
Mon 04/13 14Z 0.94 2746  93  87   9 0.04
Mon 04/13 15Z 0.92 2641  85  81   9 0.01
Mon 04/13 16Z 0.93 2538  90  91   9 0.00
Mon 04/13 17Z 1.01 2538  89  94   8 0.01

Run total areal avg QPF for the Central_Greens is: 0.87 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