NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260720_0600
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)
=== ===== === ==== ==== === === === ====
Mon 07/20 06Z 0.51 3119  78  27   9 0.00
Mon 07/20 07Z 0.52 3119  76  25   9 0.00
Mon 07/20 08Z 0.53 3119  77  36   9 0.00
Mon 07/20 09Z 0.52 3119  74  44   9 0.00
Mon 07/20 10Z 0.52 3119  72  49   9 0.00
Mon 07/20 11Z 0.50 3117  71  46   9 0.00
Mon 07/20 12Z 0.48 3017  70  48   9 0.00
Mon 07/20 13Z 0.45 3014  68  51   9 0.00
Mon 07/20 14Z 0.50 2912  67  53   9 0.00
Mon 07/20 15Z 1.04 2811  66  56  10 0.00
Mon 07/20 16Z 1.88 2709  64  51  10 0.00
Mon 07/20 17Z 3.22 2509  64  49  10 0.00
Mon 07/20 18Z 4.34 2509  65  45  10 0.00
Mon 07/20 19Z 4.43 2408  65  37  11 0.00
Mon 07/20 20Z 3.85 2308  67  33  11 0.00
Mon 07/20 21Z 2.78 2210  69  33  11 0.00
Mon 07/20 22Z 1.35 2212  68  35  11 0.00
Mon 07/20 23Z 0.65 2114  66  36  11 0.00
Tue 07/21 00Z 0.49 2117  66  32  12 0.00
Tue 07/21 01Z 0.48 2119  65  28  12 0.00
Tue 07/21 02Z 0.50 2119  64  23  12 0.00
Tue 07/21 03Z 0.53 2120  65  22  12 0.00
Tue 07/21 04Z 0.47 2120  68  21  12 0.00
Tue 07/21 05Z 0.48 2122  71  20  12 0.00
Tue 07/21 06Z 0.54 2124  76  17  11 0.00
Tue 07/21 07Z 0.55 2126  77  17  11 0.00
Tue 07/21 08Z 0.57 2127  79  14  11 0.00
Tue 07/21 09Z 0.54 2128  80  13  11 0.00
Tue 07/21 10Z 0.47 2128  85  13  11 0.00
Tue 07/21 11Z 0.38 2026  89  12  12 0.00
Tue 07/21 12Z 0.39 2027  93  11  12 0.00
Tue 07/21 13Z 0.37 2028  92  16  12 0.00
Tue 07/21 14Z 0.34 2029  92  44  12 0.00
Tue 07/21 15Z 0.27 1928  94  60  12 0.00
Tue 07/21 16Z 0.21 1928  95  73  13 0.01
Tue 07/21 17Z 0.13 1828  96  73  13 0.01
Tue 07/21 18Z 0.09 1730  97  73  13 0.03
Tue 07/21 19Z 0.20 1735  97  56  13 0.04
Tue 07/21 20Z 0.26 1637  97  84  14 0.03
Tue 07/21 21Z 0.14 1738  97  87  15 0.03
Tue 07/21 22Z 0.07 1837  97  87  16 0.02
Tue 07/21 23Z 0.18 1934  93  64  17 0.02
Wed 07/22 00Z 0.38 2034  95  71  16 0.01
Wed 07/22 01Z 0.45 2029  90  74  16 0.02
Wed 07/22 02Z 0.45 2128  87  66  16 0.01
Wed 07/22 03Z 0.59 2131  86  50  15 0.00
Wed 07/22 04Z 0.50 2130  86  53  16 0.00
Wed 07/22 05Z 0.54 2033  90  58  15 0.00
Wed 07/22 06Z 0.48 2130  91  57  15 0.00
Wed 07/22 07Z 0.59 2229  96  50  15 0.02
Wed 07/22 08Z 0.64 2326  95  65  15 0.02
Wed 07/22 09Z 0.64 2424  94  72  15 0.01
Wed 07/22 10Z 0.62 2422  92  71  15 0.02
Wed 07/22 11Z 0.53 2419  87  68  14 0.01
Wed 07/22 12Z 0.55 2420  87  59  14 0.01
Wed 07/22 13Z 0.54 2320  83  53  13 0.00
Wed 07/22 14Z 0.51 2318  80  32  13 0.00
Wed 07/22 15Z 0.58 2317  80  18  13 0.00
Wed 07/22 16Z 0.81 2216  82  29  13 0.00
Wed 07/22 17Z 1.51 2115  85  40  13 0.00

Run total areal avg QPF for the greens is: 0.32 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