NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260812_0000
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)
=== ===== === ==== ==== === === === ====
Wed 08/12 00Z 0.37 3109  74  71  13 0.00
Wed 08/12 01Z 0.49 3110  75  76  12 0.00
Wed 08/12 02Z 0.45 3113  77  77  12 0.00
Wed 08/12 03Z 0.34 3111  76  78  12 0.00
Wed 08/12 04Z 0.34 3111  73  77  12 0.00
Wed 08/12 05Z 0.40 3112  74  69  12 0.00
Wed 08/12 06Z 0.38 3111  74  66  12 0.00
Wed 08/12 07Z 0.30 3210  73  60  12 0.00
Wed 08/12 08Z 0.25 3109  73  54  12 0.00
Wed 08/12 09Z 0.26 3109  73  52  12 0.00
Wed 08/12 10Z 0.26 3109  72  51  12 0.00
Wed 08/12 11Z 0.26 3109  69  47  12 0.00
Wed 08/12 12Z 0.29 3009  67  49  12 0.00
Wed 08/12 13Z 0.32 3008  68  52  12 0.00
Wed 08/12 14Z 0.54 2808  70  58  12 0.00
Wed 08/12 15Z 1.51 2808  70  58  12 0.00
Wed 08/12 16Z 2.87 2807  69  59  12 0.00
Wed 08/12 17Z 3.50 2806  67  67  12 0.00
Wed 08/12 18Z 3.26 2706  68  81  12 0.00
Wed 08/12 19Z 2.01 2607  70  83  12 0.02
Wed 08/12 20Z 0.83 2610  77  89  12 0.02
Wed 08/12 21Z 0.57 2410  78  80  12 0.02
Wed 08/12 22Z 0.46 2609  76  66  13 0.00
Wed 08/12 23Z 0.40 2708  73  74  13 0.00
Thu 08/13 00Z 0.36 2607  73  79  13 0.00
Thu 08/13 01Z 0.48 2508  75  81  13 0.00
Thu 08/13 02Z 0.62 2510  77  88  13 0.00
Thu 08/13 03Z 0.57 2410  76  89  13 0.00
Thu 08/13 04Z 0.48 2410  75  80  13 0.00
Thu 08/13 05Z 0.39 2309  76  81  13 0.00
Thu 08/13 06Z 0.37 2210  80  90  13 0.00
Thu 08/13 07Z 0.41 2113  85  90  13 0.01
Thu 08/13 08Z 0.32 2112  86  86  13 0.01
Thu 08/13 09Z 0.27 2111  87  95  13 0.01
Thu 08/13 10Z 0.17 2009  87  93  13 0.01
Thu 08/13 11Z 0.15 2008  91  80  12 0.00
Thu 08/13 12Z 0.17 2305  96  68  12 0.00
Thu 08/13 13Z 0.23 2707  97  63  12 0.01
Thu 08/13 14Z 0.27 2809  97  69  12 0.01
Thu 08/13 15Z 0.26 2909  98  66  12 0.01
Thu 08/13 16Z 0.29 3111  98  63  11 0.01
Thu 08/13 17Z 0.26 3213  97  50  11 0.01
Thu 08/13 18Z 0.28 3214  95  45  11 0.00
Thu 08/13 19Z 0.37 3215  92  41  11 0.01
Thu 08/13 20Z 0.35 3217  88  33  12 0.01
Thu 08/13 21Z 0.24 3317  82  31  12 0.00
Thu 08/13 22Z 0.30 3218  83  32  12 0.00
Thu 08/13 23Z 0.38 3219  87  30  11 0.00
Fri 08/14 00Z 0.46 3121  85  32  11 0.00
Fri 08/14 01Z 0.50 3123  86  32  11 0.00
Fri 08/14 02Z 0.50 3224  82  32  10 0.00
Fri 08/14 03Z 0.40 3223  80  30  10 0.00
Fri 08/14 04Z 0.38 3224  79  29  10 0.00
Fri 08/14 05Z 0.33 3223  78  27   9 0.00
Fri 08/14 06Z 0.33 3222  77  29   9 0.00
Fri 08/14 07Z 0.32 3220  77  31   9 0.00
Fri 08/14 08Z 0.34 3220  76  34   9 0.00
Fri 08/14 09Z 0.35 3220  71  35   9 0.00
Fri 08/14 10Z 0.35 3221  69  45   9 0.00
Fri 08/14 11Z 0.33 3221  74  48   9 0.00

Run total areal avg QPF for the Central_Greens is: 0.17 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