NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260707_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 07/07 12Z 0.34 1113  82  52  12 0.00
Tue 07/07 13Z 0.36 1215  84  52  12 0.01
Tue 07/07 14Z 0.30 1214  80  52  12 0.00
Tue 07/07 15Z 0.26 1111  77  41  13 0.00
Tue 07/07 16Z 0.31 1111  77  40  12 0.00
Tue 07/07 17Z 0.41 1112  75  42  12 0.00
Tue 07/07 18Z 0.51 1013  74  44  12 0.00
Tue 07/07 19Z 0.57 1113  72  45  12 0.00
Tue 07/07 20Z 0.56 1112  69  49  12 0.00
Tue 07/07 21Z 0.42 1212  67  51  12 0.00
Tue 07/07 22Z 0.31 1211  65  53  13 0.00
Tue 07/07 23Z 0.24 1309  66  43  13 0.00
Wed 07/08 00Z 0.22 1208  63  37  13 0.00
Wed 07/08 01Z 0.22 1209  59  34  13 0.00
Wed 07/08 02Z 0.18 1207  58  34  13 0.00
Wed 07/08 03Z 0.12 1205  58  36  13 0.00
Wed 07/08 04Z 0.11 1204  54  36  13 0.00
Wed 07/08 05Z 0.10 1204  52  31  14 0.00
Wed 07/08 06Z 0.08 1402  52  30  13 0.00
Wed 07/08 07Z 0.07 1701  49  30  14 0.00
Wed 07/08 08Z 0.06 2101  48  27  14 0.00
Wed 07/08 09Z 0.09 2702  48  27  13 0.00
Wed 07/08 10Z 0.11 2903  50  29  13 0.00
Wed 07/08 11Z 0.11 3004  51  26  13 0.00
Wed 07/08 12Z 0.09 3104  56  26  13 0.00
Wed 07/08 13Z 0.09 3103  62  25  13 0.00
Wed 07/08 14Z 0.08 2902  67  21  13 0.00
Wed 07/08 15Z 0.13 2703  72  19  13 0.00
Wed 07/08 16Z 0.20 2603  73  21  13 0.00
Wed 07/08 17Z 0.46 2505  72  21  14 0.00
Wed 07/08 18Z 0.60 2506  72  23  14 0.00
Wed 07/08 19Z 0.58 2607  70  20  14 0.00
Wed 07/08 20Z 0.52 2507  68  16  15 0.00
Wed 07/08 21Z 0.46 2608  67  11  15 0.00
Wed 07/08 22Z 0.51 2510  70  12  15 0.00
Wed 07/08 23Z 0.59 2512  72  13  15 0.00
Thu 07/09 00Z 0.64 2514  75  14  15 0.00
Thu 07/09 01Z 0.68 2515  78  11  14 0.00
Thu 07/09 02Z 0.70 2516  80  12  15 0.00
Thu 07/09 03Z 0.71 2518  80  14  15 0.00
Thu 07/09 04Z 0.76 2620  85  21  14 0.00
Thu 07/09 05Z 0.68 2619  87  18  14 0.00
Thu 07/09 06Z 0.56 2718  82  24  14 0.00
Thu 07/09 07Z 0.53 2718  79  30  15 0.00
Thu 07/09 08Z 0.50 2718  76  28  15 0.00
Thu 07/09 09Z 0.47 2817  77  28  15 0.00
Thu 07/09 10Z 0.45 2817  79  29  15 0.00
Thu 07/09 11Z 0.43 2716  80  35  15 0.00
Thu 07/09 12Z 0.43 2715  81  42  15 0.00
Thu 07/09 13Z 0.39 2713  82  45  15 0.00
Thu 07/09 14Z 0.38 2612  79  58  15 0.00
Thu 07/09 15Z 0.40 2512  76  54  15 0.00
Thu 07/09 16Z 0.56 2513  76  51  15 0.00
Thu 07/09 17Z 0.64 2513  78  54  16 0.00
Thu 07/09 18Z 0.67 2513  81  54  16 0.00
Thu 07/09 19Z 0.70 2412  83  57  16 0.00
Thu 07/09 20Z 0.53 2412  84  57  16 0.00
Thu 07/09 21Z 0.56 2414  85  46  16 0.04
Thu 07/09 22Z 0.55 2514  84  45  16 0.01
Thu 07/09 23Z 0.56 2614  87  50  16 0.05

Run total areal avg QPF for the greens is: 0.11 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