Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260629_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 06/29 00Z 0.08 3410  60  43  14 0.00
Mon 06/29 01Z 0.07 3513  57  39  14 0.00
Mon 06/29 02Z 0.23 0115  52  37  14 0.00
Mon 06/29 03Z 0.38 0215  52  38  14 0.00
Mon 06/29 04Z 0.45 0314  55  45  13 0.00
Mon 06/29 05Z 0.40 0411  58  53  13 0.00
Mon 06/29 06Z 0.31 0309  57  61  13 0.00
Mon 06/29 07Z 0.22 0308  55  60  13 0.00
Mon 06/29 08Z 0.13 0106  55  57  13 0.00
Mon 06/29 09Z 0.12 0107  55  52  13 0.00
Mon 06/29 10Z 0.16 0108  57  44  13 0.00
Mon 06/29 11Z 0.13 0008  59  37  13 0.00
Mon 06/29 12Z 0.10 0008  60  25  13 0.00
Mon 06/29 13Z 0.10 0008  62  16  13 0.00
Mon 06/29 14Z 0.14 3506  65  13  13 0.00
Mon 06/29 15Z 0.25 3404  67  16  13 0.00
Mon 06/29 16Z 0.26 3304  65  25  13 0.00
Mon 06/29 17Z 0.38 3205  64  39  13 0.02
Mon 06/29 18Z 0.61 3205  61  33  14 0.01
Mon 06/29 19Z 0.64 3204  57  22  14 0.00
Mon 06/29 20Z 0.84 3205  54  17  14 0.00
Mon 06/29 21Z 0.56 3105  53  27  14 0.00
Mon 06/29 22Z 0.30 3104  52  29  14 0.00
Mon 06/29 23Z 0.26 3104  52  26  14 0.00
Tue 06/30 00Z 0.30 3005  54  17  14 0.00
Tue 06/30 01Z 0.38 2904  56  15  14 0.00
Tue 06/30 02Z 0.50 2705  58  16  14 0.00
Tue 06/30 03Z 0.49 2405  59  13  14 0.00
Tue 06/30 04Z 0.66 2307  60  12  14 0.00
Tue 06/30 05Z 0.74 2409  61  14  14 0.00
Tue 06/30 06Z 0.83 2411  61  18  14 0.00
Tue 06/30 07Z 0.86 2413  61  23  14 0.00
Tue 06/30 08Z 0.79 2415  59  27  14 0.00
Tue 06/30 09Z 0.82 2416  59  44  14 0.00
Tue 06/30 10Z 0.79 2416  65  51  14 0.00
Tue 06/30 11Z 0.77 2517  72  50  14 0.00
Tue 06/30 12Z 0.78 2519  79  46  14 0.00
Tue 06/30 13Z 0.72 2419  85  38  14 0.00
Tue 06/30 14Z 0.78 2519  87  44  14 0.00
Tue 06/30 15Z 0.71 2516  90  90  14 0.02
Tue 06/30 16Z 0.39 2312  82  93  14 0.05
Tue 06/30 17Z 0.40 2313  87  97  14 0.02
Tue 06/30 18Z 0.45 2314  95  87  15 0.03
Tue 06/30 19Z 0.49 2217  91  72  15 0.00
Tue 06/30 20Z 0.61 2218  89  78  16 0.00
Tue 06/30 21Z 0.68 2220  94  81  16 0.00
Tue 06/30 22Z 0.70 2222  94  83  16 0.00
Tue 06/30 23Z 0.79 2325  94  94  16 0.00
Wed 07/01 00Z 0.74 2326  94  88  17 0.06
Wed 07/01 01Z 0.83 2328  94  78  17 0.04
Wed 07/01 02Z 0.80 2330  97  80  18 0.05
Wed 07/01 03Z 0.91 2432  97  70  18 0.10
Wed 07/01 04Z 0.85 2630  97  42  18 0.10
Wed 07/01 05Z 0.74 2727  96  35  18 0.05
Wed 07/01 06Z 0.64 2823  93  52  18 0.08
Wed 07/01 07Z 0.67 2725  85  68  18 0.25
Wed 07/01 08Z 0.54 2822  83  42  19 0.09
Wed 07/01 09Z 0.59 2724  90  26  19 0.01
Wed 07/01 10Z 0.61 2825  94  11  18 0.01
Wed 07/01 11Z 0.58 2925  95   5  18 0.02

Run total areal avg QPF for the Central_Greens is: 1.01 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