NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260804_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)
=== ===== === ==== ==== === === === ====
Tue 08/04 12Z 0.47 3122  75   3  12 0.00
Tue 08/04 13Z 0.46 3122  71   3  12 0.00
Tue 08/04 14Z 0.46 3119  66   2  12 0.00
Tue 08/04 15Z 0.49 3016  61   2  12 0.00
Tue 08/04 16Z 0.54 3012  56   2  13 0.00
Tue 08/04 17Z 0.54 2910  60   3  14 0.00
Tue 08/04 18Z 0.73 2708  67   5  13 0.00
Tue 08/04 19Z 0.92 2509  72  10  14 0.00
Tue 08/04 20Z 1.24 2410  75  15  14 0.00
Tue 08/04 21Z 0.82 2510  71  19  15 0.00
Tue 08/04 22Z 0.40 2609  69  22  15 0.00
Tue 08/04 23Z 0.32 2608  67  27  16 0.00
Wed 08/05 00Z 0.28 2508  64  32  16 0.00
Wed 08/05 01Z 0.24 2508  59  36  17 0.00
Wed 08/05 02Z 0.24 2408  57  38  17 0.00
Wed 08/05 03Z 0.22 2407  56  39  17 0.00
Wed 08/05 04Z 0.21 2407  56  38  17 0.00
Wed 08/05 05Z 0.21 2407  57  38  17 0.00
Wed 08/05 06Z 0.21 2507  57  39  17 0.00
Wed 08/05 07Z 0.18 2606  56  39  17 0.00
Wed 08/05 08Z 0.14 2705  55  37  17 0.00
Wed 08/05 09Z 0.12 2604  56  34  17 0.00
Wed 08/05 10Z 0.14 2604  58  28  16 0.00
Wed 08/05 11Z 0.11 2604  59  19  16 0.00
Wed 08/05 12Z 0.11 2503  60   9  15 0.00
Wed 08/05 13Z 0.12 2404  60   3  15 0.00
Wed 08/05 14Z 0.13 2304  60   2  16 0.00
Wed 08/05 15Z 0.14 2305  60   4  16 0.00
Wed 08/05 16Z 0.17 2206  59   3  16 0.00
Wed 08/05 17Z 0.29 2307  62   1  16 0.00
Wed 08/05 18Z 0.34 2307  58   0  16 0.00
Wed 08/05 19Z 0.27 2407  50   2  17 0.00
Wed 08/05 20Z 0.29 2407  50   3  17 0.00
Wed 08/05 21Z 0.29 2408  52   4  17 0.00
Wed 08/05 22Z 0.30 2508  55   7  17 0.00
Wed 08/05 23Z 0.33 2509  62   8  17 0.00
Thu 08/06 00Z 0.37 2510  70  11  16 0.00
Thu 08/06 01Z 0.34 2610  72  16  16 0.00
Thu 08/06 02Z 0.29 2609  71  19  17 0.00
Thu 08/06 03Z 0.27 2508  68  27  17 0.00
Thu 08/06 04Z 0.27 2508  66  29  17 0.00
Thu 08/06 05Z 0.34 2510  68  33  17 0.00
Thu 08/06 06Z 0.36 2511  69  39  17 0.00
Thu 08/06 07Z 0.40 2513  74  49  17 0.01
Thu 08/06 08Z 0.40 2513  79  60  17 0.01
Thu 08/06 09Z 0.36 2512  80  62  17 0.01
Thu 08/06 10Z 0.33 2511  80  67  17 0.01
Thu 08/06 11Z 0.31 2510  80  71  17 0.00
Thu 08/06 12Z 0.27 2609  79  75  16 0.00
Thu 08/06 13Z 0.23 2607  78  87  16 0.00
Thu 08/06 14Z 0.18 2505  78  92  16 0.00
Thu 08/06 15Z 0.17 2305  80  87  16 0.00
Thu 08/06 16Z 0.24 2205  83  81  16 0.00
Thu 08/06 17Z 0.28 2204  83  76  16 0.00
Thu 08/06 18Z 0.46 2104  84  70  16 0.00
Thu 08/06 19Z 0.44 2104  83  68  17 0.00
Thu 08/06 20Z 0.29 2103  83  63  17 0.00
Thu 08/06 21Z 0.19 1904  82  59  17 0.00
Thu 08/06 22Z 0.24 2005  83  54  17 0.00
Thu 08/06 23Z 0.25 2006  84  42  17 0.00

Run total areal avg QPF for the Central_Greens is: 0.04 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