Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260629_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)
=== ===== === ==== ==== === === === ====
Mon 06/29 12Z 0.06 3511  73  34  13 0.00
Mon 06/29 13Z 0.13 0011  74  36  13 0.00
Mon 06/29 14Z 0.22 0009  76  39  13 0.00
Mon 06/29 15Z 0.51 0008  76  44  13 0.00
Mon 06/29 16Z 0.79 0006  73  47  13 0.02
Mon 06/29 17Z 0.68 0006  71  55  13 0.03
Mon 06/29 18Z 0.35 3506  69  59  13 0.03
Mon 06/29 19Z 0.20 3506  67  52  14 0.01
Mon 06/29 20Z 0.36 3306  66  41  14 0.00
Mon 06/29 21Z 0.36 3306  66  34  14 0.00
Mon 06/29 22Z 0.15 3305  63  38  14 0.00
Mon 06/29 23Z 0.09 3305  59  36  14 0.00
Tue 06/30 00Z 0.06 3405  54  20  14 0.00
Tue 06/30 01Z 0.04 3504  52   9  14 0.00
Tue 06/30 02Z 0.07 3401  53   5  14 0.00
Tue 06/30 03Z 0.21 2702  54   6  14 0.00
Tue 06/30 04Z 0.61 2704  55   9  14 0.00
Tue 06/30 05Z 0.77 2705  57  10  14 0.00
Tue 06/30 06Z 0.69 2706  58  13  14 0.00
Tue 06/30 07Z 0.60 2706  58  12  14 0.00
Tue 06/30 08Z 0.53 2706  59  15  14 0.00
Tue 06/30 09Z 0.59 2508  59  20  13 0.00
Tue 06/30 10Z 0.59 2608  60  28  13 0.00
Tue 06/30 11Z 0.60 2508  61  34  13 0.00
Tue 06/30 12Z 0.48 2407  61  38  13 0.00
Tue 06/30 13Z 0.61 2407  65  52  13 0.00
Tue 06/30 14Z 1.17 2309  71  56  13 0.00
Tue 06/30 15Z 2.00 2208  77  54  14 0.00
Tue 06/30 16Z 2.39 2210  78  65  14 0.00
Tue 06/30 17Z 1.38 2208  76  57  14 0.00
Tue 06/30 18Z 0.62 2106  73  73  15 0.00
Tue 06/30 19Z 0.30 1907  72  84  15 0.00
Tue 06/30 20Z 0.37 1910  70  89  15 0.00
Tue 06/30 21Z 0.33 1914  73  78  15 0.00
Tue 06/30 22Z 0.46 2015  80  74  15 0.00
Tue 06/30 23Z 0.50 2018  80  84  16 0.00
Wed 07/01 00Z 0.62 2121  87  85  16 0.00
Wed 07/01 01Z 0.72 2224  91  71  17 0.00
Wed 07/01 02Z 0.81 2328  95  55  17 0.01
Wed 07/01 03Z 0.88 2331  98  43  17 0.02
Wed 07/01 04Z 0.99 2434  98  38  17 0.04
Wed 07/01 05Z 0.96 2533  96  45  18 0.06
Wed 07/01 06Z 0.90 2631  95  62  18 0.14
Wed 07/01 07Z 0.77 2628  94  60  18 0.18
Wed 07/01 08Z 0.83 2630  95  32  18 0.11
Wed 07/01 09Z 0.58 2826  79  19  19 0.02
Wed 07/01 10Z 0.59 2826  91  15  19 0.00
Wed 07/01 11Z 0.54 2823  93  17  19 0.01
Wed 07/01 12Z 0.49 2822  90  17  20 0.01
Wed 07/01 13Z 0.43 2820  89  26  21 0.01
Wed 07/01 14Z 0.40 2819  86  28  21 0.01
Wed 07/01 15Z 0.38 2817  83  27  21 0.00
Wed 07/01 16Z 0.38 2917  77  21  22 0.00
Wed 07/01 17Z 0.38 2817  75  17  22 0.00
Wed 07/01 18Z 0.37 2916  72  17  23 0.00
Wed 07/01 19Z 0.37 2915  71  16  23 0.00
Wed 07/01 20Z 0.39 2814  74  31  23 0.00
Wed 07/01 21Z 0.39 2814  75  51  23 0.00
Wed 07/01 22Z 0.40 2713  77  36  23 0.00
Wed 07/01 23Z 0.44 2614  81  26  22 0.00

Run total areal avg QPF for the Central_Greens is: 0.71 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