NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260720_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 07/20 06Z 0.40 3119  77  20   9 0.00
Mon 07/20 07Z 0.39 3119  77  14   9 0.00
Mon 07/20 08Z 0.41 3119  77  18   9 0.00
Mon 07/20 09Z 0.40 3118  74  26   9 0.00
Mon 07/20 10Z 0.39 3118  71  36   9 0.00
Mon 07/20 11Z 0.39 3116  70  38   9 0.00
Mon 07/20 12Z 0.37 3115  69  44   9 0.00
Mon 07/20 13Z 0.35 3013  67  48   9 0.00
Mon 07/20 14Z 0.42 3010  66  50   9 0.00
Mon 07/20 15Z 1.17 2809  65  52  10 0.00
Mon 07/20 16Z 2.41 2607  63  49  10 0.00
Mon 07/20 17Z 4.01 2408  63  45  10 0.00
Mon 07/20 18Z 4.91 2408  63  41  10 0.00
Mon 07/20 19Z 4.84 2408  64  38  11 0.00
Mon 07/20 20Z 4.59 2309  67  35  11 0.00
Mon 07/20 21Z 3.11 2210  67  34  11 0.00
Mon 07/20 22Z 1.56 2112  64  36  11 0.00
Mon 07/20 23Z 0.76 2213  62  39  11 0.00
Tue 07/21 00Z 0.60 2116  63  32  12 0.00
Tue 07/21 01Z 0.55 2118  63  25  12 0.00
Tue 07/21 02Z 0.55 2119  62  19  12 0.00
Tue 07/21 03Z 0.58 2119  65  21  12 0.00
Tue 07/21 04Z 0.57 2120  70  22  12 0.00
Tue 07/21 05Z 0.61 2122  73  19  12 0.00
Tue 07/21 06Z 0.70 2125  78  16  11 0.00
Tue 07/21 07Z 0.71 2126  78  16  11 0.00
Tue 07/21 08Z 0.68 2127  80  13  11 0.00
Tue 07/21 09Z 0.65 2127  82  12  11 0.00
Tue 07/21 10Z 0.58 2127  87  14  12 0.00
Tue 07/21 11Z 0.52 2125  93  13  12 0.00
Tue 07/21 12Z 0.52 2127  93   9  12 0.00
Tue 07/21 13Z 0.49 2028  91  17  12 0.01
Tue 07/21 14Z 0.49 2028  92  60  12 0.00
Tue 07/21 15Z 0.40 1927  94  71  12 0.00
Tue 07/21 16Z 0.35 1927  96  80  13 0.01
Tue 07/21 17Z 0.31 1828  96  76  13 0.01
Tue 07/21 18Z 0.12 1730  97  76  13 0.04
Tue 07/21 19Z 0.08 1634  97  61  14 0.06
Tue 07/21 20Z 0.06 1637  97  86  15 0.03
Tue 07/21 21Z 0.06 1736  97  83  15 0.03
Tue 07/21 22Z 0.23 1833  97  89  16 0.02
Tue 07/21 23Z 0.37 1931  92  58  17 0.01
Wed 07/22 00Z 0.58 2031  94  76  16 0.00
Wed 07/22 01Z 0.57 2125  92  82  16 0.01
Wed 07/22 02Z 0.54 2126  87  65  16 0.00
Wed 07/22 03Z 0.71 2131  85  52  16 0.00
Wed 07/22 04Z 0.67 2131  84  63  16 0.00
Wed 07/22 05Z 0.73 2134  90  68  15 0.00
Wed 07/22 06Z 0.62 2030  92  60  15 0.00
Wed 07/22 07Z 0.70 2228  98  49  15 0.03
Wed 07/22 08Z 0.74 2326  96  58  15 0.02
Wed 07/22 09Z 0.71 2425  96  74  15 0.02
Wed 07/22 10Z 0.66 2422  96  74  14 0.03
Wed 07/22 11Z 0.56 2419  90  69  14 0.01
Wed 07/22 12Z 0.60 2419  90  57  14 0.01
Wed 07/22 13Z 0.62 2420  87  56  13 0.00
Wed 07/22 14Z 0.56 2318  83  30  13 0.00
Wed 07/22 15Z 0.65 2318  83  21  13 0.00
Wed 07/22 16Z 0.73 2216  85  34  13 0.00
Wed 07/22 17Z 1.59 2116  89  42  13 0.00

Run total areal avg QPF for the Central_Greens is: 0.35 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