NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260804_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 08/04 12Z 0.64 3022  75   3  12 0.00
Tue 08/04 13Z 0.64 3123  70   2  12 0.00
Tue 08/04 14Z 0.63 3020  64   2  12 0.00
Tue 08/04 15Z 0.63 3017  59   2  12 0.00
Tue 08/04 16Z 0.64 2913  55   4  13 0.00
Tue 08/04 17Z 0.64 2812  59   9  13 0.00
Tue 08/04 18Z 0.81 2710  66  15  13 0.00
Tue 08/04 19Z 1.01 2610  69  18  14 0.00
Tue 08/04 20Z 1.24 2511  71  21  14 0.00
Tue 08/04 21Z 0.79 2510  68  26  14 0.00
Tue 08/04 22Z 0.47 2610  66  29  15 0.00
Tue 08/04 23Z 0.37 2609  63  33  16 0.00
Wed 08/05 00Z 0.30 2509  59  37  16 0.00
Wed 08/05 01Z 0.27 2509  55  38  17 0.00
Wed 08/05 02Z 0.26 2509  54  39  17 0.00
Wed 08/05 03Z 0.23 2508  54  39  18 0.00
Wed 08/05 04Z 0.22 2508  55  38  18 0.00
Wed 08/05 05Z 0.21 2507  56  38  17 0.00
Wed 08/05 06Z 0.22 2508  58  38  17 0.00
Wed 08/05 07Z 0.20 2607  58  39  17 0.00
Wed 08/05 08Z 0.18 2606  59  39  17 0.00
Wed 08/05 09Z 0.16 2605  59  38  16 0.00
Wed 08/05 10Z 0.17 2606  59  34  16 0.00
Wed 08/05 11Z 0.15 2605  60  27  16 0.00
Wed 08/05 12Z 0.14 2505  61  18  16 0.00
Wed 08/05 13Z 0.13 2405  62  12  15 0.00
Wed 08/05 14Z 0.13 2305  63   7  15 0.00
Wed 08/05 15Z 0.13 2205  64   5  15 0.00
Wed 08/05 16Z 0.15 2206  64   3  16 0.00
Wed 08/05 17Z 0.27 2307  65   2  15 0.00
Wed 08/05 18Z 0.31 2307  60   1  16 0.00
Wed 08/05 19Z 0.26 2306  52   1  16 0.00
Wed 08/05 20Z 0.26 2306  51   2  17 0.00
Wed 08/05 21Z 0.28 2407  53   3  17 0.00
Wed 08/05 22Z 0.28 2407  57   5  17 0.00
Wed 08/05 23Z 0.29 2508  64   6  16 0.00
Thu 08/06 00Z 0.32 2409  72   8  16 0.00
Thu 08/06 01Z 0.31 2509  74  12  16 0.00
Thu 08/06 02Z 0.27 2508  72  15  16 0.00
Thu 08/06 03Z 0.26 2508  70  22  16 0.00
Thu 08/06 04Z 0.27 2508  67  23  16 0.00
Thu 08/06 05Z 0.33 2509  68  28  16 0.00
Thu 08/06 06Z 0.38 2511  68  34  16 0.00
Thu 08/06 07Z 0.43 2512  71  44  16 0.00
Thu 08/06 08Z 0.42 2612  74  57  16 0.00
Thu 08/06 09Z 0.37 2611  75  57  16 0.00
Thu 08/06 10Z 0.32 2610  77  63  16 0.00
Thu 08/06 11Z 0.31 2610  79  64  16 0.00
Thu 08/06 12Z 0.25 2608  78  68  16 0.00
Thu 08/06 13Z 0.22 2606  78  77  16 0.00
Thu 08/06 14Z 0.16 2504  79  80  16 0.00
Thu 08/06 15Z 0.13 2204  81  76  16 0.00
Thu 08/06 16Z 0.17 2205  83  72  16 0.00
Thu 08/06 17Z 0.19 2104  83  66  16 0.00
Thu 08/06 18Z 0.29 2104  82  64  17 0.00
Thu 08/06 19Z 0.30 2104  81  62  17 0.00
Thu 08/06 20Z 0.19 2103  80  55  17 0.00
Thu 08/06 21Z 0.13 2004  80  52  17 0.00
Thu 08/06 22Z 0.16 2005  82  53  17 0.00
Thu 08/06 23Z 0.17 2006  83  46  17 0.00

Run total areal avg QPF for the greens is: 0.00 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