Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260126_0000
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 01/26 00Z 0.29 1226  85  90 -13 0.00
Mon 01/26 01Z 0.36 1229  85  93 -12 0.03
Mon 01/26 02Z 0.40 1131  86  93 -12 0.03
Mon 01/26 03Z 0.40 1128  86  93 -12 0.04
Mon 01/26 04Z 0.46 1030  85  91 -12 0.05
Mon 01/26 05Z 0.46 1029  85  91 -12 0.04
Mon 01/26 06Z 0.54 1030  86  90 -12 0.03
Mon 01/26 07Z 0.57 0931  87  93 -13 0.02
Mon 01/26 08Z 0.53 0927  88  93 -13 0.01
Mon 01/26 09Z 0.52 1027  88  92 -12 0.01
Mon 01/26 10Z 0.44 1024  89  90 -12 0.01
Mon 01/26 11Z 0.41 1023  90  91 -12 0.01
Mon 01/26 12Z 0.38 1122  90  93 -12 0.01
Mon 01/26 13Z 0.35 1121  89  93 -12 0.01
Mon 01/26 14Z 0.36 1121  90  91 -12 0.01
Mon 01/26 15Z 0.32 1219  91  94 -12 0.01
Mon 01/26 16Z 0.28 1216  92  93 -12 0.01
Mon 01/26 17Z 0.19 1313  92  92 -11 0.01
Mon 01/26 18Z 0.08 1510  92  92 -11 0.01
Mon 01/26 19Z 0.03 1608  93  93 -12 0.01
Mon 01/26 20Z 0.08 1905  94  96 -12 0.02
Mon 01/26 21Z 0.20 2306  91  97 -13 0.02
Mon 01/26 22Z 0.29 2508  90  97 -14 0.02
Mon 01/26 23Z 0.43 2712  89  95 -15 0.02
Tue 01/27 00Z 0.64 2916  88  89 -16 0.02
Tue 01/27 01Z 0.80 3018  88  85 -17 0.01
Tue 01/27 02Z 0.75 3020  91  83 -18 0.01
Tue 01/27 03Z 0.65 3020  91  82 -19 0.01
Tue 01/27 04Z 0.53 3123  92  80 -20 0.00
Tue 01/27 05Z 0.50 3125  90  78 -20 0.00
Tue 01/27 06Z 0.48 3126  91  70 -19 0.00
Tue 01/27 07Z 0.49 3127  88  62 -19 0.00
Tue 01/27 08Z 0.53 3028  88  53 -19 0.00
Tue 01/27 09Z 0.51 3027  87  44 -19 0.00
Tue 01/27 10Z 0.48 3027  80  34 -19 0.00
Tue 01/27 11Z 0.43 3025  67  25 -18 0.00
Tue 01/27 12Z 0.37 3023  55  18 -18 0.00
Tue 01/27 13Z 0.38 3022  58  22 -18 0.00
Tue 01/27 14Z 0.38 2919  72  45 -18 0.00
Tue 01/27 15Z 0.38 2814  76  69 -18 0.00
Tue 01/27 16Z 0.36 2611  81  81 -18 0.00
Tue 01/27 17Z 0.38 2410  78  81 -18 0.00
Tue 01/27 18Z 0.50 2312  74  81 -18 0.00
Tue 01/27 19Z 0.47 2214  82  79 -18 0.01
Tue 01/27 20Z 0.65 2316  80  78 -18 0.01
Tue 01/27 21Z 1.14 2319  83  80 -19 0.01
Tue 01/27 22Z 1.26 2321  89  78 -19 0.00
Tue 01/27 23Z 1.69 2522  94  72 -19 0.01
Wed 01/28 00Z 1.77 2623  90  68 -19 0.00
Wed 01/28 01Z 1.06 2623  84  65 -19 0.00
Wed 01/28 02Z 0.91 2624  84  67 -18 0.00
Wed 01/28 03Z 0.85 2623  87  72 -18 0.00
Wed 01/28 04Z 0.87 2623  89  74 -19 0.00
Wed 01/28 05Z 0.72 2720  86  73 -18 0.00
Wed 01/28 06Z 0.71 2719  87  74 -19 0.01
Wed 01/28 07Z 0.73 2820  86  72 -19 0.01
Wed 01/28 08Z 0.75 2820  87  71 -19 0.01
Wed 01/28 09Z 0.83 2822  87  67 -19 0.00
Wed 01/28 10Z 0.94 2725  81  60 -20 0.00
Wed 01/28 11Z 0.88 2827  72  60 -20 0.00

Run total areal avg QPF for the Central_Greens is: 0.56 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