Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260629_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 06/29 06Z 0.08 0005  67  72  13 0.00
Mon 06/29 07Z 0.05 3404  67  66  13 0.00
Mon 06/29 08Z 0.10 3305  69  65  13 0.00
Mon 06/29 09Z 0.16 3206  73  64  13 0.00
Mon 06/29 10Z 0.15 3308  75  58  13 0.00
Mon 06/29 11Z 0.13 3309  74  47  13 0.00
Mon 06/29 12Z 0.09 3310  71  33  13 0.00
Mon 06/29 13Z 0.06 3410  70  21  13 0.00
Mon 06/29 14Z 0.07 3408  72  20  13 0.00
Mon 06/29 15Z 0.12 3406  74  20  13 0.00
Mon 06/29 16Z 0.36 3307  72  25  13 0.00
Mon 06/29 17Z 0.41 3308  71  37  13 0.01
Mon 06/29 18Z 0.29 3408  66  35  13 0.02
Mon 06/29 19Z 0.43 3307  63  25  14 0.01
Mon 06/29 20Z 0.39 3307  58  14  14 0.00
Mon 06/29 21Z 0.34 3307  55  13  14 0.00
Mon 06/29 22Z 0.12 3406  52  16  14 0.00
Mon 06/29 23Z 0.10 3307  52  26  14 0.00
Tue 06/30 00Z 0.13 3306  52  18  14 0.00
Tue 06/30 01Z 0.24 3205  54   7  14 0.00
Tue 06/30 02Z 0.25 3003  57  14  14 0.00
Tue 06/30 03Z 0.45 2504  60  14  14 0.00
Tue 06/30 04Z 0.48 2405  62  16  14 0.00
Tue 06/30 05Z 0.59 2307  63  12  14 0.00
Tue 06/30 06Z 0.77 2409  64  11  14 0.00
Tue 06/30 07Z 0.88 2511  65  12  14 0.00
Tue 06/30 08Z 0.85 2513  63  13  14 0.00
Tue 06/30 09Z 0.84 2613  65  16  13 0.00
Tue 06/30 10Z 0.88 2614  65  21  13 0.00
Tue 06/30 11Z 0.69 2613  67  36  14 0.00
Tue 06/30 12Z 0.65 2514  71  46  14 0.00
Tue 06/30 13Z 0.63 2513  74  42  14 0.00
Tue 06/30 14Z 0.65 2413  78  55  14 0.00
Tue 06/30 15Z 0.73 2312  81  59  14 0.00
Tue 06/30 16Z 2.03 2313  80  70  14 0.00
Tue 06/30 17Z 2.34 2211  78  69  15 0.00
Tue 06/30 18Z 0.84 2016  74  84  15 0.00
Tue 06/30 19Z 1.24 2119  78  72  16 0.00
Tue 06/30 20Z 2.80 2219  85  79  15 0.00
Tue 06/30 21Z 1.00 2219  82  81  16 0.00
Tue 06/30 22Z 0.83 2220  87  55  17 0.00
Tue 06/30 23Z 0.82 2323  93  43  17 0.00
Wed 07/01 00Z 0.91 2425  94  39  17 0.00
Wed 07/01 01Z 0.90 2426  97  36  17 0.01
Wed 07/01 02Z 0.88 2526  97  34  17 0.01
Wed 07/01 03Z 0.94 2529  98  48  18 0.05
Wed 07/01 04Z 0.81 2629  92  49  19 0.12
Wed 07/01 05Z 0.81 2630  92  30  19 0.03
Wed 07/01 06Z 0.82 2631  89  43  19 0.02
Wed 07/01 07Z 0.73 2729  89  40  20 0.02
Wed 07/01 08Z 0.72 2728  92  24  20 0.02
Wed 07/01 09Z 0.67 2727  91  15  20 0.01
Wed 07/01 10Z 0.57 2826  85  15  21 0.02
Wed 07/01 11Z 0.48 2823  77  19  21 0.02
Wed 07/01 12Z 0.37 2920  67  24  23 0.01
Wed 07/01 13Z 0.32 2917  63  31  23 0.01
Wed 07/01 14Z 0.30 2815  62  33  23 0.01
Wed 07/01 15Z 0.31 2815  61  35  23 0.00
Wed 07/01 16Z 0.30 2814  62  40  23 0.00
Wed 07/01 17Z 0.29 2712  65  38  23 0.00

Run total areal avg QPF for the Central_Greens is: 0.40 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